Hi Uriah,
I recently upgraded, but didn't want to spend a fortune and went for this:
- i5 2500K @4.3GHz with my old water cooling stuff (you'd be able to reuse your Koolance kit and nice PSU of course)
- Cheap Motherboard (I never crossfire/SLI) MSI USB3/SATA6 - $300 bundled with the i5
- ATI 6950 2GB, unlocked and overclocked as a 6970 - $210
- 128GB SSD SATA6 Gbps for OS and favourite games (I use something called 'Steammover' to move between my favs between the 2TB set and the SSD) - $120
- 8GB DDR31600 - $35
All together, and using my existing 3 monitors (eyefinity!), case and other bits cost around $700 USD to upgrade. Plus I had Win7 x64 already, which is needed for the 8GB ram.
I get good frames, plus of course the ability to play games other than COD nicely too

. A lot of sims (DCS, RoF, GTR etc) work great in large resolutions across the 3 screens too, which makes it a nice upgrade.
Hope that helps, in that it's not cutting/bleeding edge but well good enough to burn through the current state of the sim. Obviously, a fair amount of fiddling knowledge and bargain hunting is included as well.
Edit: Should have said, up here in the Frozen North in Vancouver, I paid in Canadian Dollars (they're like proper dollars, but with a hint of
maple syrup and very sticky tar oil).
Edit 2: For GPU, I find this useful, as in always try to buy the best single chip solution from the 3rd row whenever upgrading:
http://www.tomshardware.com/reviews/gaming-graphics-card-review,3107-7.html