Well, I had the small Graphire years ago with my PC and when I went Mac and it wasn't compatible I upgraded to the 6x8 Intuos. I would say if he's willing to spring for it, get a 6x8. I like it much better. I wouldn't want bigger though. Your actual tablet size is considerably bigger than the dimensions of the drawing surface, and the bigger ones get HUGE! 6x8 is a really nice size.
EDIT: was just looking at their website and that would be close to the Bamboo Medium. The dimensions are a little different now to be more like a widescreen monitor I think. And I actually had meant to say that... now that I have a widescreen, I wouldn't mind a new tablet that's widescreen, but it's not a huge deal.