Caseend.com is a nice little helper in that perspective, but also, there always is the SFF PC Master List 
The A4-H2O needs thorough planning, because if you pick the wrong AIO, you could be annoyed as much as I was 3 weeks ago, ie. the tubes getting nastily bent, plus having to kind of force everything in place.
Just switched to the trusty S400 V2, and aside a little side panel closing issue (AMD sockets seem to be 1 - 2 mm taller than Intel), I am absolutely happy I did the switch
Maybe this case might be something for you as well? I guess the Gigabyte Aorus 6800XT is a three slot card, isnt it? The S400 V2 supports 3 slots, up to 335 mm length, so this should work quite nice. Obviously this would mean using a low profile air cooler, so if you're concerned about less toasty CPU temps, thats probably out of question. On the other hand: Is it more toasty than a 7950X?
But if its just about going for an AIO-focused case, but smaller, then the Meshroom S / Meshlicious is always a solid choice
Another option might be the Raijintek Ophion (Evo) (16L / 18L).
cu, w0lf.
