I bet the 7950 would be in your range and provide a good upgrade over the 5850. At the very least, when the new cards are finally available, you should be able to catch a good sale on a 6970...(same with nvidia and the 670 pushing down the 570 - though that may be a bit farther out).
You could go with a GTX560 SLI or an HD 6950 Crossfire at that price
HD 7950 will be $450 about €400 in his price, and maybe higher.
@OP, if you're limited by your budget and can't wait, your best option is a GTX 570 or HD 6970 even though they might cost more.
Well, I CAN wait. I was planning to buy a new one this week, but I can easily wait the 9th of January.
But why do you say those cards might cost more than the 7950? I believe that a 570 is around 300-350€.
Anyway, considering your suggestions, I think i will wait and go for the 7950.
I said that HD 6970 or GTX 570 might cost more than Your Budget.