I'm happy to announce I successfully installed a 980 AIO on a Titan X. I have a 3rd Titan X coming in the next day or two and 3 AIO units in total. I will post pics and benchmarks then.
I did a simple benchmark test with Heaven 1.0. I have both cards overclocked to about 1400mhz with max power target, temp target, overvolt, ect.
My normal Titan X I ran the GPU fan at a static 100% which is around 4,800RPM (LOUD)
My AIO Titan X I ran the GPU fan at a static 20% which is around 1,000RPM (quiet)
I'm using a Corsair SP120 quiet edition running at a static 700RPM for the AIO radiator (quiet)
My AIO Titan X runs 20C+ cooler and obviously 10x quieter than the other Titan X running. I'm sure the difference would be 30C+ if both fans were running the same speed. More to come in a few days.