Good choice, 5850 is beat, matches against the GTX 285 and beats it most of the time i believe from what i remember.
Uhhh yea ASUS is fairly good in GPU's, they make solid computer parts in general like their mobo's and all that. The 5850's are only referance boards right now so don't worry about the brand so much, they are all the same and manufactured the same.
ASUS is good tho, buy from them....i can't wait till they come out with non-reference boards, ASUS is probably gonna use their new tech like they did in their 4890, with the SUPER ML cap and all that....say they could achieve 300% overclocks and the aftermarket heatsink was good too from what i read about it.