Well, I'll add my 2 cents.
The most convenient and best performing case (IMHO) for building small-mid size system with a custom loop would be the Fractal's Define S and Define Nano S. (as you can see from my setup, I do put my money where my mouth is
Phanteks Enthoo Evolv ATX and ITX are a an option if you are ready to compromise a bit on performance and size for a better look.
All above options have more than enough rad space to quietly cool anything you can throw in. 480 rad surface (as a single unit or split across 2) is enough for a loop with single GPU (of course CPU and whatever else). For dual GPU 600-720 rad surface is more than enough.