I have the XMS pro series PC4000, and also TwinX PC3200LL. Huge difference on the timings they can run. Also, it affected ability to use Gaming enhancement on an IS7 (PC4000 can't use it at all, the PC3200LL could run the top setting called F1). If you are running default DDR400 speeds, the low latency ram is far better. If you are overclocking and want to keep the mem/fsb to a 1:1 ratio, then you need the PC4000. I just bought the PC4000 for overclocking and it's good for that. But I was dissappointed on how it limited my bios tweaks so much at DDR400 speeds. I wish I had that Crucial Ballistics memory that seems to be able to handle both well (aggressive timings at DDR400, but also OC to DDR500)
Anyway, no need to run your ram higher than 2.7v UNLESS you are trying to get stable at high mem/fsb speeds(overclocking). Pumping 2.9v or more into that PC4000 of yours is not going to help it run 2-2-2-5 timings, but could kill the ram if you push it too high. If 2.7v is stable, leave it there. If you are trying to find the highest speed your mem can run at, then boost it to 2.8v when needed.
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