With your water cooling, and the access you want, you need to go big in the case - whatever the design.
Frozen CPU sells the cable to use two psu's, together. View Atlas Folder Part 2 on YouTube for a view of it. (Atlas uses two psu's for each mobo/gpu set up). Here:
http://www.youtube.com/watch?v=7F3XE1-d_rw
In tower cases, I'd suggest: HAF 932, Xigmatek Elysium & Rosewill Blackhawk (last two are the same basic case), and CubiTek's HPTX Tank (more expensive, but all aluminum). I have the latter, and there are pics of it in my Tanker thread, in the folding team forum.
Commonly, you have a top front drive cage in these cases, and a lower removable drive cage, below it. (non-removable one's can still be removed, that's what saws and such are for). Use the upper cage for the system drives, and remove the lower section - now you have a very large area to put your w/c equipt. in.
The bench/test cases looked a bit small, but maybe it's just the lack of a reference size in the pics. A vented top should be OK, as long as your cat doesn't pee into it. I agree that an open top of any kind, would be a disaster. I like their wide and low stance however. A cat jumping up on it, would never tip them over.
In the folding team forum, there is a thread on 4p cases and case modding. There is a semi-custom case builder in there, with a bare bench case picture, who might be able to work up something just for you - lots of options. Prices seemed good too. Handle was "Spotswood", iirc. Take a look.