yea, thats definitely a very nice choice. if i hadn't gone with the 78gt for performance i probably would've gotten the 68gs, it seems like the best price for performance deal besides the 78gt.
anyways, i have a 3800+ and it runs VERY well im totally satisfied with it. im sure it won't bottleneck you at 2ghz with the vid quality way up, and im also sure that you could get to 2.4ghz without adding a ton of heat.