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I've noticed changing the MCH Strap will change any ram settings that are on Auto, specifically the 5th timing on (to the last one). Usually your ram only specs out the first 4 timings. (ie 9-9-9-24)
Changing MCH Strap (in my case) I noticed the other timings were adjusted higher or lower. Timings were lower on 1333 than they were on 1600.
Likewise I had problems booting and could not run memtest86 with MCH Strap on 1333, obviously because it set the extra timings lower than what my ram used. I changed MCH Strap to 1600, I've had no problems since. I've also had no problems with disappearing ram since turning MCH Strap off Auto and putting B2B CAS Delay back to Auto (0) (which turns it off according to CPU Tweaker).
Two different things there....
MCH Strap is one thing, Uncore multiplier is another.
Your uncore multiplier should technically be no higher than 2x your ram divider. IE if your ram divider is 2:8, your uncore should be 16. (since 8x2=16)
If you're running 2:10 your uncore might be 20x but you generally need a lot of QPI/Vtt voltage (depending on what the bios calls it) to run a 20x uncore. Most OC guides tell you to lower uncore to 16x because it will take uncore out of the equation on stability (and also allow you to use a lower Vtt voltage). Some people try to run higher uncore frequencies (17x is generally usually stable; 18x is hit or miss)...AFAIK uncore doesn't really affect F@h at all and running a higher uncore than 16x does take more Vtt so essentially it's not worth it.
Your ram dividers are fairly self explanatory....however in most bioses (including that of the SR-2), the dividers do not give a x:y divider ratio, they give a speed. If speed is given, you can safely assume that the speed is always based on the stock 133mhz frequency (in general most bioses all base any speed setting on 133mhz). IE in the SR-2, the ram settings are as follows:
DDR-800 (divide 800/133 and you get 6, so that is 2:6 ram divider)
DDR-1066 (1066/133=8, so 2:8)
DDR-1333 (1333/133=10, so 2:10)
I don't recall off the top of my head if the SR-2 has a DDR-1600 but obviously that would be 2:12.
The MCH Strap setting does not use the 133mhz base speed for what it says (as far as I can tell). IE setting MCH Strap to 1600 uses a generic 1600mhz speed settings for CAS latencies and such.
To answer your question - if you want to OC your ram, you would change the ram speed setting to increase the divider. The end result will be your base clock (bclk) multiplied by the 2nd number of your divider (ie 6, 8, or 10). IE in my case I'm running 200bclk, with my 1333 ram oc'd to 1600 I was using the 2:8 divider and therefore my ram speed setting was DDR-1066 which is the 2:8 divider. Now I'm running DDR3 2000, same bclk, so I changed the setting to DDR-1333 (2:10, 200x10=2000 for the ram).
Obviously depending on your ram it might work, it might require more vdimm voltage, or it might not work at all if you oc too high. You can usually get a few hundred mhz free on ram with no voltage bump, but depending on what your bclk is, changing the divider might push the ram too far. You say you're running 200bclk; if your ram is 1600 your divider should be 2:8. However you probably won't be able to change it to 2:10 and get your 1600 ram to run at 2000. If you're running 1333 @ 2:6 divider and you change it to 2:8 like I did to run @ 1600, that will probably work no problems. Going from 1333->1600 is fairly easy and a safe bet; going from 1600->2000 is a 400mhz oc for the ram and may not be possible without more vdimm or looser timings (ie higher # timings like 10 or 11 instead of 8 or 9).
Hope this helps clear up your questions.
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