Why are you looking to upgrade? It doesn't look like a bad build to me, especially if you play all your games on max settings. Don't waste your money.
If you absolutely have to spend some cash, you could get $300 5850 or for $400 get a 5870. But what's the point? If you wait until games actually use DX11, you could find the cards cheaper, have a better selection, and won't have to play the "who can order first" game.