auto is fine, but if you start overclocking then you might want to up the fans speed slightly. see how loud you can take your fans, it never hurts to run the GPU fans on the high side, as more cooling never hurt anything in fact it could ideally help in the long run. I keep my GPU fans at 50% up until 65C where it then curves up to 100% at 80C (this might be loud for most people) get MSI afterburner or another overclocking tool like precisionX and see what fan curve works best for you.