I have been looking at upgrading my 4890 because it is just too loud and hot.
I have not seen a viable upgrade for it yet that does not cost over $300.
If the 480s are cooler running now then I would also suggest them for the gamer.
TBH I would keep your 285s for now and wait till 6000/500 series comes out. There are only 5 games out right now with DX11, and another 6-10 due out this/next year. Of course civilization V is coming out next month with DX11... that might have me down grading to a DX11 setup soon