I am looking forward to seeing part two. My system was put together as a "bridging" system; recycling parts that had been used to upgrade a previous computer, and initially that included the X850 Pro video card.
Ultimately, I don't really think that going beyond a DX9 card with a socket 939 mobo and cpu is really worth it. Having said that, I'm sure that it would work great in my system and give a small boost, but the trouble is the CPU, even as an overclocked dual core, is still "underpowered".
The only games that I have trouble with ARE CPU-intensive, such as Supreme Commander. Mind you, I have a philosophy of starting at maximum and then working my way down; but once you're CPU-bottlenecked, you find that lowering the settings on the game doesn't make it run any faster.
Here's the core of my system, such as it is:
CPU: Athlon64 4200+ X2 (base 2.2 Ghz, OC'd to 2.8 GHz)
RAM: 2 GB OCZ w/copper heatspreaders, set to run at 333 DDR (166) and the FSB OC'd to 255 from 200 Mhz to achieve overclock. (Ram nets out running at 423 Mhz DDR, and the CPU gains ~27.25% clock speed).
Video: Sapphire X1950 Pro AGP, 512 MB GDDR3
Motherboard: ASUS A8V-MX MicroATX
This is an extremely stable overclock, and even at full load, the CPU doesn't really get that hot. I've never had drive issues or problems with the video card, other than it can overheat under extreme pressure. And I just use the stock coolers for both.
I feel that it's actually good that the games now use the CPU more now... it always felt stupid that your CPU investment was much less important than your graphics controller.