Thanks for your answer.
Ah yes i didn't see that it was Dt with the coolant temperature, my bad. But in some way that's even worse because the coolant temperature does not stay stable when the GPU gets hotter if the cooling is not enough so the ambiant air would actually be a better point of reference in that case.
And of course the rad/fans come into play even without throttling: if the coolant can't evacuate enough heat into the air then it becomes warmer and so the GPU gets warmer, which give false results on its real cooling capabilities.
I'm not an advocate of LM for the average end user either, but since you're an editor at TPU you're definitively not an average user and it would make your test more accurate
Also my Dt was with 1.1v. With 1.2 it's pretty close to that and since it's a 1080ti its also consuming 70W more than a regular 1080. Just saying that 45°C or more for a 1080 under custom watercooling is just wrong. That's the kind of temperature you can get with an AIO system. You shouldn't be above 35°C with a proper setup.