that xfx one is a really good deal, especially with free shipping.
there are already a few games that have dx11, but you need windows 7 for it
http://en.wikipedia.org/wiki/List_of_games_with_DirectX_11_support
as for better driver support, that constantly comes. hell i still update my drivers for my 8600 GT - so its never ending, and as time goes on it will get better and better. i was also going to get a 5750 but now that my budget is higher im springing for a 5850. in any case i don't think the added performance for the 5X70 cards are worth the added price. that card will be killer though
edit: just thought i'd post this, with my 5850 im getting is one of the first dx11 games to be released which is dirt2. as per
THIS article you can see the differences, and as per
THIS article you can see the performance hits. for being the second released dx11 game i think these numbers and image qualities are extremely promising for dx11.
in the first article they sum up that it depends on the user, but they do not really think the gain in image quality justifies the loss of performance yet, however this is again only the second dx11 game released up to this point.
dx11 will surely be more utilized in the future, making for a huge image difference (i notice it pretty heavily in dirt2 already) and with again added driver support etc we will see the performance loss become less and less, and as it stated...its already MUCH less than the loss that accompanied dx10 with its release.
very promising indeed. i for one cannot wait for STALKER call of pripyat