If you want to extreme overclock with water cooling, grab a custom bios and flash it. I did that with my 980ti and it allowed me to overclock to 1530mhz rather than the 1400mhz I got on my old bios. The only thing is it puts alot of heat into my loop since the voltage is at 1.274.
My temps while stressing my gpu and cpu before the overclock were 65c on cpu and 42c on gpu. My cpu is overclocked to 5ghz.
Now with the gpu overclock, my cpu is at 78c and my gpu is at 58c.
Like I said, it pumps alot of heat into my loop. But if your card is cooled by itself, then youll be good