I'd go with the 5900XT, cause its gonna be in the same league as the 5800U without AA/AF, and faster with high levels of AA/AF.
But most importantly, the 5800U is friggin loud, even at idle, while the 5900XT is very quiet.
Even better, go with the eVGA 5900SE (400/700) $189 which is faster than the XT
http://www.newegg.com/app/viewProduc...130-179&depa=0