Nah get the 7850, if you wind up upgrading to newer mobo and CPU later, that card will still be decent, even if your performance is limited SOME, better video is not a bad thing.
It's a good price point too, I spent $400 on mine, at the time I think the 7850 was still $250ish.
Video card is the one part I have system hopped more than once.
Looking at specs, I forgot to mention need for PCIe 16x v2.0 slot for compatibility, looking at specs of your motherboard, didn't say what revision, that could be a problem if it's 1.x and the card doesn't support 1.x, not a definite or anything.
I would go here and confirm that, when they are open: http://www.service.asus.com/#!consumer/csn9
^if in USA or Canada.
I tried to, unfortunately now closed.
Found a thread where someone put in a 7750 and said it worked great, so it's probably a non-issue.
Apparently, that mobo can handle the Phenom II x4 945 CPU with the right revision/bios update, also.