Video card dollar per frame per second values

I’ve been trying to figure out if I should buy a new card and if so, what, and if so, what I should spend. But since I have an LCD, I’m looking for something particular — the best performance at 1920×1200. This turns out to be kind of hard to figure out if you read gaming sites, which run a bunch of tests at different resolutions without current pricing

For December 26th 2008, frame rate divided by dollars (how many $ you’re spending to get each frame-per-second, lower is better), using a variety of random benchmarks done at high quality and high AA/AF filtering. My methodology is terrible, etc etc.

Dollar per FPS, 1920x 1200 gaming

4870 $6.2
GTX 260 $7
4850 X2 $7.4
GTX 280 $10
4870 X2 $11

Data pulled from Firing Squad, Sharky Extreme, Anandtech

It’s weird to me that more sites don’t do exactly this kind of comparison. If you’re in the market for a new card, it’s kind of assumed that you’re either in the “mainstream” market at $100-150 or whatever they define it as, the “enthusiast” $300 or the “have an insane amount of money” at $500+.

But say you could spend any of those amounts but really, really don’t want to. What’s the best value here? Are you better off buying the best $100 card on the market every year, or spending $500 now and sticking with it for much longer?