i'm using 4x512MB OCZ 4400 (DDR550) but so far my max prime95 stable OC has been 240MHz (DDR480). my volts in bios are set to 2.8v (using p4c800-e dlx on 3.2GHz prescott @ 3.84) i've booted into windows and run 3dmark using 4 dimms at 4GHz but it's not prime stable.
from my experience, you're bound to lose a few MHz when using 4 dimms as opposed to only 2. further, 4 dimms may pose stability problems etc. especially if you don't have a good enough PSU. you'll have to check your individual dimms but OCZ's love volts (usually rated for 2.8v but some will go as high as 3.2 using OCZ's boosters - but don't take my word for it, check it out)
also i recently upgraded from a 3.0GHz northwood (manufactured jun 2003) to a 3.2GHz prescott (october 2006), the older NW core limited my OC to only 225 stable, so it's very possible for the CPU to be the limiting factor for your OC and not the RAM.
Last edited by munz778; Feb 24, 2007 at 02:09 AM.