If he's running Linux, will he be playing games?
If not, grab the 5200 ultra, as it should be available at a lower price than the 4800. Or indeed, just get a straight 5200. If he's a game player then get the 5200 on a budget and the 4800 if he can afford it. the 4800 is going to do almost everything better except maybe anisotropic filtering or DX9 stuff and even then it will be a toss-up.
Look here for a benchmark comparison
http://www4.tomshardware.com/graphic...311/index.html
Elad.