No, not siginificantly. There were some tests back in the day of the GF1/GF2 where overclocking the AGP bus was necessary on the 440BX motherboard with "B" P3 CPU's, and apparently there was some performance benefit of an overclocked AGP bus, but right now all overclocking the AGP bus does is make the video card run a bit hotter, and possibly decrease stability if your card can't handle it (generally, nVidia cards cope with a higher AGP speed better than ATI ones).