you might want to gather some information about the poor fermi performance in 3d apps.
the fermi architecture has a hardware restriction when it comes to 2sided faces and will perform very very bad.
i also wanted to upgrade my old 9800GTX but as i had (yes had) a GTX470 at work to see that the performance is not even close to the 9800GTX i had to rethink my upgrade choice.
NOTE: i need 2 sided for the work i do so if you can work with 1sided only it might not be a problem for you.
and since quadro cards are no option for me as well i bought a GTX285 today which is at this point the best card you can get if you work with 2 sided faces.
sure there would be the option of AMD cards but their drivers have always been very weak in opengl apps and from what i read so far it didnt get any better...
here are some links where you can catch up about the performance issue with the fermi cards.
here a thread i started because of the 470 performance http://blenderartists.org/forum/showthread.php?t=191597
and one on cgtalk: