I'm looking to build a computer with a cheap C2D chip now, but upgrade in the future when the prices of the quads come down. Will the soon to be released QX9650 be the fastest chip for a 775 mobo, or will a faster chip come out before Intel changes sockets again?
Yes, they will. 775 is wider used than 478, and yet 478 got prescott processors. People will have the chance to gradually move from 775, else, if they will need to upgrade board, cpu, ram and maybe even graphics at the same time, they might go on to AMD. AMD lost because of this. Intel knew beforehand this could happen, but even if they did not, they learned. You can't build core architecture without being able to learn (just in case Intel is run by some kind of AI).