We are moving away from the question but I don’t like that this solution deemed dead because of that wrong statement. Yes pumps don’t like bobbles but you of course place the reservoir before the pump to catch them. My D5 live happily after 4 year with a standing radiator outside the PC case. This is the best way to reduce temperature of the case and the cooling water.
Well, I agree that we moving away from the topic, but as you guys see is close related to why we need the case able to fit 420 rad.
Regarding fitting a radiator outside the case, that's my choice and I want to have it inside the case. No need to look untidy, and anyway my partner is a cleaning freak, so might damage it while cleaning. Better be inside and safe.
Regarding the safety of AIO, in my life haven't seen a showering radiator, even tho I have opened and modified myself a couple, for better performance.
Back to the topic, someone suggested Thermaltake Core X9. Seems good, even the price is affordable, the only stock has amazon where is white only.