Ask any company that sells ATi cards what happens when you OC. Tech support will tell you any overclocking voids the warranty.
Now ask Evga or XFX and you'll get a different response. They'll say they'll replace your card if it dies while being overclocked and that you should increase clocks gradually.
My personal experience with both Evga and XFX backs up what others have said; they do indeed officially support end user overclocking and HSF replacement.
If you resell your cards XFX is definitely a solid choice because you can transfer your lifetime warranty to your buyer. That builds value.
Now ask Evga or XFX and you'll get a different response. They'll say they'll replace your card if it dies while being overclocked and that you should increase clocks gradually.
My personal experience with both Evga and XFX backs up what others have said; they do indeed officially support end user overclocking and HSF replacement.
If you resell your cards XFX is definitely a solid choice because you can transfer your lifetime warranty to your buyer. That builds value.