Every modern GPU has a "target" temperature that it tries to maintain by manipulating fan speeds (and past a certain point, clock throttling). 67C is lower than I'd expect for a target temp. Most people agree that GPUs are ok in the 70-80C range. Most GPUs I've worked with have a target temp somewhere around 75C +/-
I've discussed this with others before, but depending on the time remaining on your warranty (and whether or not this would ACTUALLY void your warranty) I had great success removing my GPU's heatsink and re-applying TIM. Lowered my temps from 85C to 73C and fan speeds decreased significantly (roughly 1000rpm reduction). The process isn't any different that re-applying TIM to a CPU, you're just using half as much TIM since the chip is only about half as big. The heatsink on the majority of GPUs is still just held on by the 4 screws around the chip itself. The rest of the screws are used for holding the backplate etc on.