Me, your 1000 Mhz CPU is plenty fast enough. The bottleneck in your system now is that V3. Isn't it also limited to 16 bit color?
When I was building my new system I realized that I had to balance CPU and video card performance because depending on the type of game you are playing EITHER can be the bottleneck. For example, many racing games and flight sims are very CPU dependent. But some action games like Quake3 are very video card dependent while Unreal Tournament is more CPU dependent.
My goal was to have high frame rates at 32 bit color, high resolutions with maximum 'eye candy' visual effects. Overall, I've achieved that. I get demo1 average 84 fps in Q3 at 1280x1024, 32 bit color, all effects max, high quality audio. Also playable at 1600x1200 with 60 fps demo1 average. In UT I get 75+ average framerates in deathmatches at 1600x1200, 32 bit color, all effects max.
I know I'm rambling on a bit but my point is that I think your video card is going to be a bottleneck if its too slow regardless of how fast the CPU is.
I'm not sure what your question really is now. Definitely return the GF2 Pro that you paid $250 for. That's way too much. You already know you can get a Pro at newegg for around $130 (32MB version). I wouldn't bother with the $170 64MB Pro. The extra 32MB isn't really going to do much for you right now. Either the $130 Pro or $242 Ultra will offer a much better performance match to your 1 gig CPU. It comes down to how much money you want to spend and what resolutions you want to play at. If you deathmatch only at 800x600, 16 bit color then the Pro would be plenty fast enough. If want max resolution and eye candy then go for the Ultra.
Its seems you are leaning toward a new mb and CPU. Its your decision of course but if I were in your situation I would upgrade the video card. As I said earlier, you CPU is already fast enough for now.