That wasn't what I said either. I said those two resolutions would get me better or equal frame rates than 640x480 and 800x600.there's absolutely no way a game will run better at 1280x1024 than it will at 1024x768
Lower resolutions are more cpu intensive while higher resolutions are more gpu intensive. You can look at it as two exponential curves like I have drawn below. As you get closer to the extremes in resolution, CPU or GPU become the bottleneck. Finding the optimum mix gives you max fps.