Just another thought…and it probably won’t be the culprit in this setup, as you have an “open” case (something I’ve never actually seen before, so not sure of the pro’s and con’s of that)…but the actual placement of your cpu AIO could be the culprit in some setups?
In my previous PC, the CPU AIO was on the top of the case, blowing air form inside the case through the rad and back OUT the top of the case…good in theory, because it’s taking the heat produced by the CPU and expelling it OUT of the case…however, if you have a beefy GPU that’s also producing a lot of heat…you’re also trying to cool the CPU by using the hot air that’s already inside the case.
In my current build, I instead have the radiator at the side/front as an intake…so it’s taking cold air from OUTSIDE the pc case, running that through the radiator and helping to cool the liquid before it returns to the CPU to help cool that…better for CPU, but possibly worse for other components like the GPU, as any heat carried from the CPU TO the radiator is then getting blown INTO the case.
If your rad is at the top though, even with an open case, I imagine the hot air produced by the GPU will rise and be blown through your cpu air rad.
I’m no expert, but this is my thinking anyway.
I think provoked prawn on youtube did a good video about this subject a while back.
Like I said though, not sure exactly how this all works with an open case :s