u should be able to oc 2500k, gtx470 for c3 mp, but just don't oc em to max limit.
i'd probably run the cpu @ ~4ghz(if u have good hsf) n run the gpu at stock speed.
try ~8hr prime95 torture test for cpu stability when u oc(check temp too), n ~8hr valley benchmark loop for cpu/gpu stability. http://secure.gamesas.com/forums/viewtopic.php?f=65&t=66223
should be able to run c3 mp without any issue if ur system can pass prime95 n valley.