Darn, caught him before I could. The C3 stepping has a better IMC, so you can run your RAM up to 1600-1800mhz more stable. It also uses less voltage for the same clocks, so instead of the 4ghz wall most C2 CPUs hit, a C3 965 can hit 4.2ghz @ 1.5V. Just remember to look for the 125W version of the 965 or if you want to be extra sure, check that the model # ends with "...MBOX"(applies for 955 C3 as well). The C2 steppings end with "...IBOX".