Please help me with overclocking and RAM/MBoard compatibility

[Bogdanov89]

I am having trouble understanding all this stuff about overclocking RAM and motherboards that support it.
For my new gaming PC i can buy either:
• DIMM DDR3 2x8GB 2400MHz Kingston HyperX Savage CL11
• DIMM DDR3 2x8GB 1866MHz Kingston HyperX Savage CL9
For my new motherboard i can choose between:
• LGA1150 Z97 ASUS SABERTOOTH Z97 MARK 2
• LGA1150 Z97 ASUS Z97-PRO GAMER
• LGA1150 Z97 MAXIMUS VII RANGER
• LGA1150 Z97 ASUS Z97-AR
My CPU will be Intel i7-4790K and my PSU is a 750w Seasonic SS-750AM2, GPU is Nvidia GTX 980.
I understand that CL9 is better than CL11, but the entire overclocking thing baffles me.

What really confuses me is the following:
1. Sabertooth motherboard does not seem to support 2400MHz RAM - but it does support 1866MHz RAM without overclocking, or am i mistaken?
2. The other 3 mother boards support up to 3000+MHz RAM, but they do not support 1866MHz RAM without overclocking?
3. I do not understand how RAM overclocking works, do i sacrifice my CPU performance (or something else) when i overclock my RAM to 2400MHz?
4. If the 2400MHz RAM is left to work at only 1866 MHz, does it still have CL11 - or does the latency drop to CL9 since it runs on 1866MHz?
5. Which motherboard would be the best choice if i want to run a 1866MHz RAM at CL9?
6. Which motherboard would be the best choice if i want to run a 2400MHZ RAM at CL11?
I am not able to understand which RAM should i pair up with motherboard for maximum performance?
The prices are very similar, so money is not the problem here - i just don't understand which RAM+Motherboard would give the best performance in games like Battlefield 4 (64 multiplayer).

(side question): what is better for a single Nvidia GTX 980 GPU, a PCI (32-bit) slot or a PCI-Express 16x slot?

 

[case sensitive]

RAM frequency has almost no effect on gaming performance above 1600MHz when you are using a dedicated gpu.

Regarding your first two questions: The memory controller is located on the CPU so this dictates what memory frequencies are considered overclocking.
In the case of the 4790k, anything above 1600MHz is overclocking (but up to 2400 should require little/no tweaking).

3: With Haswell (4790k etc.) CPU's, higher memory frequencies can limit the maximum core OC in some cases.

4: you can manually set cas latency (CL) along with other timings. If you ran 2400MHz ram at 1866 then you could set it to CL9.

5/6: Makes no difference.


In conclusion: I recommend 1866MHz ram (especially if it is cheaper) because there will be no noticeable improvement in gaming performance if you were to buy 2400MHz.
As for motherboard, go with whichever meets your requirements (I/O etc.) or wait for other people to post some recommendations (as I don't own any of the boards you have listed).

As for your side question: you need to use a PCI-Express slot for the 980, modern graphics cards are not compatible with PCI slots.

 

[Tsumi]

RAM: Whichever is the cheaper of the two. The difference in those specs isn't going to matter for Intel CPUs. Above 1600 MHz is overclocking the IMC, so there is a slightly better chance you will get 1866 CAS 9 over 2400 CAS 11. The 4770k is only rated for 1600 mhz.

Any particular reason you're hung up on Asus?