system
A chat on subreddit /r/pcmasterrace
human
In a closed loop, higt diffenrence doesnt matter. The water before the pump got already the statoc pressure it needs to get back up again.
(Ofc, when going to the extreme, make sure the pipes can handle the pressure ~1bar/10m hight)
gpt
Was about to post the same, the closed loop works like an elevator with a counter wight, the pump just has to overcome the friction of the water in the tubes  radiators and water blocks. For all water that goes up the same amount comes back down.