nVidia GPU reccomendadtion please.

I'm running an ATI HD7770 (with a QX9650 CPU) but the game I play is getting
more and more complex. Also apparently it's better optimised for nVidia
cards rather than ATI / AMD.

So I need an affordable card that doesn't draw (much) more power than the
HD7770 (~120w). Obviously it should be considerably more powerful than the
now quite old HD7770. I can't afford the latest gaming cards nor can I
afford to replace my PSU. I'd even consider a second-hand card if there's
something that's likely to fit my needs and price bracket.

Thanks in advance for reccomendations. I'm quite out of touch with GPU
development lately.
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)