The gtx4xx series scale almost linearly. I meant to run the benchmark scene while we were there, but just didn't have a chance to do it. A lot also depends on the scene. There was a lot of glass, especially in that shot, which dramatically lowers one's megasamples.
BTW I just looked at how many views that video has recieved so far and it is the highest of the Siggraph vids at just under 1000 views. Animation Mentor is the closest behind it with around 950 views.
System 1: EVGA gtx470 1280Mb and MSI gtx470 1280 in Cubix Xpander for Octane, AMD 945, 4Gb Ram
All systems are at stock speeds and settings.