What are the Performance Differences between the Q8200 And E8400?

Q8200 or E8400

That link is useless as an answer to the OP's question. The entire thread is a debate with no definite conclusion.

As to which processor is better, it depends entirely on the programs you plan on using and how many threads they can utilize.
Here's a comprehensive article about core utilization among various different programs. Note that in all of the gaming benchmarks, there was a considerable boost when moving from 2 to 3 cores, but not when transitioning to 4 cores.

For your needs i'd imagine the processor hierarchy would look something like this.

Q9550>E8400=Q6600>Q8200

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

Sometimes you feel like a core, sometimes ya don't.
q8200 has cores
e8400 don't

q8200 has deep dark chocolate, coconut and crunchy cores too !
e8400 has deep dark chocolate and chewy coconut, ooo !

Sometimes you feel like more cores, sometimes ya don't !

Unless you are someone who upgrades your cpu multiple times over the year with your existing motherboard, I say get the quad. I went from a single core skt 939 cpu to my existing quad. I could have gotten a dual or triple core that would be faster in existing games, but I upgrade my cpu once every few years. Quad made sense for me because I'm banking on applications catching up to utilize quads which makes my purchase last for awhile, especially with oc'ing.