
Here's some 3Dmarks benchmarks to give you a good idea of the diffs on an AthlonXP1800+ (gfx card: total marks, game1 high detail FPS, game2 high detail FPS, game3 high detail FPS, nature DX8 FPS):
1024x768x32:
4200: 10500, 54, 109, 66, 57
4400: 11000, 57, 115, 72, 46
4600: 11000, 54, 116, 68, 66
1024x768x32xAA:
4200: 7400, 42, 77, 50, 30
4400: 7600, 44, 76, 53, 49
4600: 8200, 46, 86, 53, 36
1600x1200x32:
4200: 6000, 46, 62, 46, 19
4400: 6500, 47, 67, 46, 21
4600: 7200, 50, 74, 51, 23
1280x1024x32xAA:
4200: 4700, 39, 47, 32, 16
4400: 6000, 45, 60, 40, 26
(dubious result, but only match)
4600: 6000, 43, 61, 42, 20

For all benchmarks I quote the average result, not the top which is usually a fake or simply unobtainable for 99.9% of people even with the same setup. The exception is the 1280x1024x32xAA scores which only had 1 result submitted for each card!