New graphics card!

The 5850 and 5870 are pretty slim pickings when it comes to their availability. Honestly if you have the funds for a 5850 just wait for them to come in stock and pick one up. The 5770's performs slightly under a 4870, but does have the DX11 that you are looking for. A 5850 performs significantly better and is worth the $300.

Just wait for the 5850 to come in stock and get it. You can wait for the Nvidia DX11 cards, but I have a feeling they won't be cheap, but they also might drive down the ATI cards in price. I would wait until you are just about ready to buy the game.

You CPU will be a limitation no matter what graphics card you install. That will just free up more GPU power for sparkly stuff, like AA/AF.

Im going to like buy a new motherboard and *** next year maybe^^
So its pointless to buy a 5850, because my processor will bottleneck it?

Limitations (I also hate the term bottleneck) are not totally negative, they are just there, as jay2tall mentioned, all systems have limiting hardware, it is not such a hindrance as the term "Bottleneck" makes it out to be.

Your CPU may limit how many FPS you will get in certain titles, allowing the GPU to do more work per frame, IE AA/AF. That is why I use Vsync on every game that I can. It is like emulating a CPU limitation, but slowing down the graphics so that the card isn't going bugsh!t crazy trying to blow out 200fps, generally allows more stable use of higher textures, anti-aliasing, AF, shadows etc etc.