Mmmm, well, usually the card should not run at such high temperature on idle, but a temperature of 65º C on load is quite good. You should throw some GPU stress test to the card to see if the image has artifacts (or if everything goes down) before you can be really sure, but you can push it harder. How hard? That depends, overclocking takes its time, and it's better to proceed in small steps. Unless you're really going to overclock it to the max, I don't see any need for a water cooling kit, you know, GPUs usually do not overclock as good as CPUs, and particularly ATI cards. And GPUs withstand really high temperatures.
Yeah, you can mess with the BIOSes of the cards, but never got there.