http://www.xbitlabs.com/articles/video/display/geforce-gtx-480_6.html#sect1
There's really no reason to go from a 295 to a 480.
Are you finding your GTX 295 to be insufficient? Or just too loud?
Honestly at this time I would recommend waiting for the next gen of ATI cards to be announced in October/September, this will drive down prices significantly IMHO (both nvidia and ATI cards). This should also force nvidia to release a non crippled Fermi chip (480 is gimped to a certain extent to keep it within power limits).