CPU vs GPU: which do I upgrade for TF2?

[whiplash000]

...wow that was kinda poetic

So I posted a thread here asking for advice on which GPU to upgrade my system to. I mentioned that EVGA would replace my 8800gt later on in the thread. That got me thinking... Since I no longer HAVE to replace my GPU, should I upgrade my CPU instead? Here's my current specs:

Motherboard: ASUS p5n-d
CPU: Intel Pentium Dual-core e2140 (currently OC'd to 2.8ghz, gone as high as 3.2 stable)
RAM: 4GB G.Skill ram
GPU: EVGA 8800GT
Monitor: SCEPTRE 24" monitor (1920x1200) (drool)
PSU: Thermaltake 430w power supply

Look at the thread I linked to before to see that I decided if I'm gonna upgrade my GPU, it's gonna be a Radeon HD 5850. That, plus a new power supply, will cost me around $350 to $400.

On the CPU side, I have my eye on either a Core 2 Duo e8200, or one of the Core 2 Quads (model suggestions?)

Remember that my primary game is TF2, which I heard was very CPU dependent. So... CPU or GPU?

 

[whiplash000]

TF2 is CPU dependent but it likes a fast dual core CPU. So at stock the E8200 would more then likely outperform the q6600 but you can always OC the Q6600 to reach similar levels. You would then also get the advantage in games that utilize multi-cores.

TF2 would perform similar to L4D in this benchmark
http://www.anandtech.com/bench/Product/53?vs=58

P.S. upgrading your GPU for 1910x1200 would also make sense.

The reason I can't upgrade both is because I'm poor... I have to upgrade stuff one thing at a time. So what quad core has the best price/overclocking potental ratio right now?