50 C is pretty good. If you want lower temperatures you can:
1. Put a different fan on the radiator, or two fans in push/pull...you will have to drive them from your motherboard or a fan controller. If you drive off your motherboard, remember that the typical maximum current for motherboard fan headers is 1 amp...so check the current rating on your fans before you use a 2, 3, or 4 way PWM splitter.
I personally use two Corsair ML120 fans on my each of my 3 AIOs (one for CPU, 2 for GPU - I used the 1080 hybrid kit to mod an AIO onto my Titan X Pascal).
2. Run your GPU AIO radiator as intake into the case. The temperature will be cooler as the air across the radiator is the cooler room air versus the warmer internal air of your case. The downside is that you will be bringing in warmer air to cool your case components.
On my case, I run:
- 1 CPU AIO as intake (2 fans in push/pull)
- 2 GPU AIO as intake (2 fans in push/pull on each)
- 2 140 mm fans as intake
- 3 140 mm fans as exhaust
Each of my Titan X P cards stay below 45 C...and these cards draw a lot more power than a standard 1080. Internal temperatures are great (memory and all other components stay below 38 C).