With 4 sticks of ram, Winchester or older core will run at 333mhz 2T timings. Venice, San Diego, Manchester, Toledo, and opterons, will run 4 sticks at 400mhz 2T timings. 4 sticks will work fine in dual channel(assuming it's socket 939, since 754 is single channel). 2T timings give around a 3-5% performance hit in most cases, so not really that big a deal.