Getting ready to buy one of the 21.5" iMacs. Three things separate the entry from the better system. One is CPU speed, but that is negligible. Another is hard drive space, and I debate whether that is a big deal at this point. But it also has a video chip and video memory difference. So I ask, what is the difference between these video chipsets? My use: Surfing TV recording (but not as a media server) Photo work (modest, family stuff) Video editing (again, modest family video snippets) Thanks!