Just to clear up a myth that seems to go around as well. Running ram at 2000mhz is very easy with a 975, for the simple reason that you can set the ram divider to 2000mhz and just use the multi's to get your desired clock. The reason that it's hit and miss with a 920 is because to get to 2000mhz you have to be running a BCLK very near to the limit of the QPI link (4000mhz). With the 975, you only need to be running a BCLK of 133 to run the ram at 2000mhz.
You still need a chip capable of 4000Mhz Uncore which I would've thought is by no means a guarantee even with a 975.