What is your resolution? At 1080 P and less on one Monitor should last quite awhile as long as the rest of your system is up to the task. Hard to say with new games though, they are getting more demanding all the time. I have two gtx 660's in SLI which is about the same as 1 GTX 680 and they start to struggle with Crysis 3 Beta.
Yes 1080p, I would of thought they last more than 3 years, also the warranty do I need to register it now or do I only do that when I actually get a fault to replace it