I have an EVGA GTX 280 that runs at 75C (with fan at 100%) while playing games but I want to over clock it. Problem is, when it's over clocked it gets to 85-90C (with fan at 100%). Is there a way I can get my GTX 280 to run cooler? I can't afford water cooling I read that it's possible to open the GTX 280 and apply newer, nicer, thermal paste (I would use Arctic Silver 5).
Applying newer and better thermal paste is a good idea and shouldn't be risky.
You can also replace the cooler altogether if you desire but that would cost you about $50 and that $50 + ebaying the GTX 280 could surely net you a GTX 460 which would be a better idea.
Another thing to consider is case airflow. Your case may have places to mount more fans which will help bring down temps and those should be rather cheap and help the whole system rather than just the card.