For your needs i'd imagine the processor hierarchy would look something like this.
I'm using a Q6600 at 3.2ghz myself and i'm very pleased with it. And to be honest at stock it was quite powerful anyway, i had no issues with games being slow.
Personally for you i'd grab the Q9550, it's one step up from the Q6600 in tech. It's faster at a lot of applications, sometimes 40% faster due to the added instruction set. So as far as i know the video encoding would get a nice boost
Crysis will be the only game from your list that, MAY, benefit from more then 2 cores. I noticed a lot of activity across all my cores when i played a while back. The rest will play very well on just one of the Core 2 cores to be honest. Might get a small boost from a 2ndcore.
The biggest boost will be in multi-tasking and heavily threaded apps. And some games, hopefully more new ones will make better use of extra cores. Although it already seems like 2 cores feed a single decent graphics card full already