Hi, i would stay away from watercooling, becouse (assuming you are not experienced with making watercooling rigs):
- Expensive to set up properly
- Possible problems with the rig itself which you often cant handle by yourself. ( i had mine made with best parts possible, handled it like my own child and still had a leak)
- Difficulties with selling the GPUs after few years
and the biggest drawback-> if you run into any problems with CPU or motherboard or any of your 4 GPUs you can't fix it ourself which freezes your work during a project.
My main workstation has a problem with motherboard and it needs to be replaced, the problem is that everything is watercooled and the person that created the rig does not have time to fix the problem ( it was about 6 months ago ) so i am left with a very expensive piece of industrial furniture
The only good thing is that the rig will be very silent and cool, but as i wrote before, if you do not have any solid and trustworthy person that knows how to set it up and manage for the next couple of years dont go with watercooling. Also, check if your motherboard and case can fit 4 GPUs and at least 1500W PSU.