I am collecting parts for a new computer, and am interested in advice on AMD video cards that will take advantage of Vegas Pro 11 (I've seen a number of threads of NiVidia, but not so much on AMD).

Personally, I'd stick with nVidia and walk away from AMD. In working with many people and their GPU issues, it appears the AMD's have more issues than the nVidia's. In either case, though, make sure you're using a CURRENT driver - not necessarily the one that comes with the card. You need to go directly to the manufacturer's website and download the current version.

Yeah, I've learned to always get the latest drivers. I've used both nVidia and AMD. The last year or so I've had good luck with AMD. I've seen enough posts to have a good idea of what nVidia cards to look at for Vegas 11 - trying to see if anyone has used AMD with success.