How much of a performance difference between X16 * 2 lanes vs. X8 * 2 lanes?

Asacolips

Limp Gawd
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Dec 4, 2008
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[H] did a comparison, and the answer was pretty much no difference, for practical purposes. x4/x4 made a small dent, but even that wasn't horrible.

x16/x16 vs x16/x8
x16/x16 vs x8/x8
x16/x16 vs x4/x4

[edit] I also have no clue as to why I'm post #1 now. Maybe it's just displaying like this on my pc. For reference, the op is KickAssCop, and it's his question.
 

Spiko

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Nov 20, 2009
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When I was reasearching for my setup where I have a choice of 16x 16x with no air flow or 16x 8x with air flow for the most part it looked to be a 3-5 fps drop so I went with the configuration that didn't stack my cards so bad. I'm not sure about 8x 8x thought. I'd expect a performance hit there.

In most cases SLI/Crossfire are more trouble than they are worth. At this point your best bet is to wait for a 7 series and get a single card.
 

Forceman

[H]F Junkie
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In terms of SLi or Crossfire performance how much of a difference does it make? I would be interested to see comparisons in benchmarks (real world or synthetic) in gaming. I have a board that only supports X8 * 2 lanes. Is it still worth doing SLi or CFX?

Did you check the links in the OP? [H] tested this last year and the answer is that it doesn't make much difference.

Edit: How is my quote of your post ahead of your post?
 

Asacolips

Limp Gawd
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Dec 4, 2008
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Did you check the links in the OP? [H] tested this last year and the answer is that it doesn't make much difference.

Edit: How is my quote of your post ahead of your post?

KickAssCop is the op, not me. Somehow his post date got dropped back about 30 minutes. So he has the original post, but the replies are showing up before his.
 

KickAssCop

Supreme [H]ardness
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In terms of SLi or Crossfire performance how much of a difference does it make? I would be interested to see comparisons in benchmarks (real world or synthetic) in gaming. I have a board that only supports X8 * 2 lanes. Is it still worth doing SLi or CFX?

Also what is a PCI e lane splitter. I have no clue since I have never done SLi or Crossfire before.

Thanks.
 

KickAssCop

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lol what happened in this thread.
So is the verdict that there is no difference?
 

Crest

Limp Gawd
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In most cases SLI/Crossfire are more trouble than they are worth.

What? It's not like it's 2006. My SLI 580's have been a dream. No issues. Sure that's anecdotal, but multiGPU setup issues are much rarer now.
 
Joined
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Messages
789
[H] did a comparison, and the answer was pretty much no difference, for practical purposes. x4/x4 made a small dent, but even that wasn't horrible.

x16/x16 vs x16/x8
x16/x16 vs x8/x8
x16/x16 vs x4/x4

[edit] I also have no clue as to why I'm post #1 now. Maybe it's just displaying like this on my pc. For reference, the op is KickAssCop, and it's his question.

the forums has been fucked up for a week now as far as post order. I have noticed this in many other threads as well. I'm guessing something is wrong with the time sync, so if you are in an earlier time zone than someone else, instead of the forum automatically using its own time, its using each individual users local time making the posts out of order
 

supafreak

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Aug 7, 2011
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Hey guys, I just setup 2x 5870s in Crossfire and have been pleased thus far. I really didn't like how close the cards had to be though. I went with the two full speed slots, but boy are the cards like microns apart. They may well be getting enough air (my case is pretty well ventilated) but it just hasn't been sitting right with me ;)

I have an ASUS P6T which has:

2 x PCIe 2.0 x16 (dual x16, blue)
1 x PCIe 2.0 x16 (x4 mode, white)

From what I am hearing I may as well try the x4 mode slot and get better cooling? I don't think losing a few FPS will be noticeable if that is all I am losing.

What do you guys think?
 
Joined
Dec 23, 2010
Messages
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Hey guys, I just setup 2x 5870s in Crossfire and have been pleased thus far. I really didn't like how close the cards had to be though. I went with the two full speed slots, but boy are the cards like microns apart. They may well be getting enough air (my case is pretty well ventilated) but it just hasn't been sitting right with me ;)

I have an ASUS P6T which has:

2 x PCIe 2.0 x16 (dual x16, blue)
1 x PCIe 2.0 x16 (x4 mode, white)

From what I am hearing I may as well try the x4 mode slot and get better cooling? I don't think losing a few FPS will be noticeable if that is all I am losing.

What do you guys think?

I'd say run some benchmarks now and let us know how it turns out when you switch. I really don't think you'll miss much unless your running a 2500x1600 monitor with Metro 1333 or something like that.
 

linuxdude9

Gawd
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Dec 25, 2004
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It would be nice to see a 16x and 4x comparison -- since maybe having one card at the faster speed may cause more of a problem.
 

geant90

Limp Gawd
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Aug 6, 2011
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The difference is not much at all, will post video link later. gtx 580 sli 16x 16x vs 16x 8x / 8x 8x was 1 fps difference.
 

KickAssCop

Supreme [H]ardness
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Messages
7,354
Many thanks guys. Seems like I do not need a motherboard change at all. I also game at a low resolution so it should really not affect me. Appreciate your comments!
 

Ducrider748

Limp Gawd
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Jul 25, 2011
Messages
308
You will see a difference in fps in a high end card running a fast cpu.With the gpu's on themarket today you will not see much difference.The 8x pci-e lanes can transmit enough data that the average gamer will not see it.
 

Xeon User

Weaksauce
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Aug 23, 2011
Messages
93
There is no difference between running dual-GPU solutions on x16-x16 vs x8-x8. This is because even the high end cards like the 590 and 6990 still haven't managed to fully saturate the PCI-E bandwith. By the time we see this happening PCI-E 3.0 will be the standard.

A good estimate would be a 1-2% peformance loss at the most. Unless the MoBo manufacturer provides an on-board lanes like the NF200 chip to the P67/Z68 chipset, your cards will run at x8-x8. Most users prefer the x8-x8 configuration over something like a NF200 chip because adding another bus for the data to travel through(in layman's terms) adds more latency and usually ends up having the same or worse performance numbers than just using the lanes provided by the chipset.

That being said, x8-x8 multi-gpu should not deter you from purchasing a MoBo provided that you won't tell the difference in real life bandwith for most modern cards, but if you are going to be running two big boys you definately want your cards to at least run at x8 speed.

When running x8 opposed to x16 my scores dipped a few points, but we are talking about scores in the thousands.
 

supafreak

n00b
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Aug 7, 2011
Messages
7
FWIW I bought a longer crossfire cable and moved my second card to the 3rd slot on my ASUS P6T, ran like complete ass and locked up the computer. Moved it back to the second slot and while the top card is quite a bit hotter than the bottom one it at least runs good. I am sure YMMV but figured it might be useful for you guys to know my experience. I bought a 4 pack of fans just in case, guess I will be installing those this weekend to hopefully keep my cards cool. No stability issues at all, just running about 15 degrees hotter on the top card than bottom, not ideal IMO.
 

Dosobye

Limp Gawd
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Jul 29, 2010
Messages
397
Oh shit, Hi Kickasscop!
long time(I lost my old account haha)

Im sure its been answered already but there is no difference, hell not much noticeable difference even with a 4x slot.
 
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