Actually it depends. The 470 is better than a 5850. Without PhysX it wins. There's not many games that have PhysX acceleration, but I've played several with a dedicated GT240 (close to a 9800GT, maybe closer to a GTX) and the usage is usually quite low. Maybe 15%. The one exception is in Batman AA, where it's at times been as high as 50% due to all the cloth and smoke PhysX stuff but only at some scenes.
I think in general the GTX470 is going to be faster even in PhysX games. Batman, the 5850 + 9800GT should win.
Although, if you're asking because you have a 9800GT laying around, you can use it as a dedicated PhysX card with the 470 too.