The big thing here is going to be whether you're using multi-threaded software that can take advantage of multiple cores or not.
The Q8200, which happens to be the processor I have in my home machine, will probably be a little slow in single threaded tasks because of its lower clock speed.
If you want to play modern games and encode video, I would go with the Q8200.
Im building a new desktop for general use, but i also planned on using it to record, mix, and master audio for my band. I cant find any info on whether the programs i plan on using are multi-threaded or not. If i use Windows OS, ill use Magix Samplitude Producer Edition, and if I use Mac OS ill use either GarageBand or LogicStudio.
From what Ive heard, the Dual Core would be sufficient in speed for the tasks im looking to accomplish, but Im always open to new suggestions.
They're about the same price, so you pretty much have a choice between 2 really fast cores, and 4 slightly slower cores that will rock in multi-threaded apps (you'd need 3 or 4 threads for it to out-shine the E8400).
LGA 775 is EOL. So you may want to look into a good compromise, the AMD Phenom II X3 720: