if you dont have money, then its OK to go, else nVidia didnt showed so called PERFORMANCE Architectural desing in FX series, GeForce 4 was better than FX (earlier versions), and now 6800 series is rock solid.
as 5700 chip came at very last, so it must have some good features than olders (5200, 5600, 5800), which I am sure had made it worthful to buuy.
if u r getting that, better buy from a reliable manufacturer (Asus. MSI)