Well, you certainly don't NEED an upgrade, but since you say you upgrade every couple of years, you must be on the money.
A GTX780 would do the trick. You could consider buying an identical card and going to KroshFire (failed joke there :P).
Your PSU should be able to handle it.
Consider a GTX760 SLI too, as these cards are scaling pretty good now a days.
Thanks for the response, at present my aft mentioned ghetto motherboard doesn't support sli/crossfire but I will definitely look into the 760 - the 2 year gpu upgrade thing is a bad habit from back in the voodoo 2 days.