You want a $550 AMD card, sounds like you are asking for us to tell you to buy a 7970. So go buy one. Mine is pretty sweet.
Part of my reasoning for buying a 7970 and not something like a 6950 or 6870 for less money is the upgrade path... about a year or 18 months when my 7970 doesn't cut it as much, can buy a second 7970 and kick ass again. Now if I had bought a 6950, the upgrade route to crossfire is cheap yes, but not as future proof. And starting out with SLI or crossfire is the worst upgrade route for 18+ months down the road, you will have two GPUs that aren't worth a whole lot.