Casey Kelley :
You will absolutely get more than a 1 or 2 degree difference. I have a feeling you've never done custom H2O cooling because then I think you would understand why one does it.
from stock air. sure. from AIO, no. i put some Noctua A12x25 fans on my h100i and on my hybrid 1080ti.... thats as good as it gets.
i have followed many youtubers like linus and jayz2cents. they have routinely admitted that custom cooling is for looks. if not for the sake of being custom into a custom case for instance. they have many vids comparing, and unless you are doing some crazy stuff like mounting the rad completely outside the case in a push/pull with top of the line fans.... you wont see a difference.
thats the only reason i have held off on a kit. i have built a setup a few times on ek's site configurator. but that price just keeps holding me back because i know my gpu and CPU might only get MAYBE 1 degree cooler. not to mention my old h100i has never needed to be flushed/cleaned. so thats a perk.
if you want to drop temps, delid! thats where you get the best drop, and its only like $10 for some liquid metal.
dont get me wrong, if i had the money (AND TIME) i would do it. but there are many things i will spend 1k on first. before wasting it for 1 degree.
1) a second 1080ti hybrid
2) replace my 1tb nvme 960 evo raid, with new 970 1tb pros for a 2tb raid
3) replace my 1tb 850 evo raid with 960 pro 1tb drives for a 2tb raid
4) replace my 1tb nas drives with 2 to 4tb drives
those are just some things i want to get done , and that will give me way better pc experience then a custom loop.