E8400 vs Q9550

If you'll use the extra cores yes.

It will add a fair bit of longevity to your system

Maybe. I'd just crank that 8400 up to 4 and call it a day.

If you render, sure.
If your rig is just for gaming, no.

and the extra L2 cache.

Thanks for the input guys. Well my E8400 would end up going into my server and fold on it 24/7.

Still though, I'm mostly a gamer. Really that's all I do on this rig, but then again this chip would also allow me to fold on two dual-core VMs.

Hmm, such a choice.

A quad at 4ghz is always better than a dual at 4 ghz.

If I can get to 3.6GHz I'll be happy. I already know my board isn't much of an overclocker to begin with.

if you can get 475 fsb on it, you're good.