I would think that you should be good for at least a couple of 3 years at that res. I use mine at 1920x1200 and it runs everything I can throw at it. I haven't even overclocked it yet! And from the reviews I read it can easily overclock to GTX480 speeds. And the best part of it all is the quietness of the cooler!
you're probably good at that res for 2 years at high settings, maybe another 2 years at medium and another year at low res... so liek a 5 year lifespan if you're willing to keep using it for the long haul .. beats mine.. my low end 8500gt only made it 2 and a half... btu it was under 50 bucks and overclocked heavily