Personally I wouldn't trust a water rig I'd built myself for that amount of kit, but if money is really no object, what the hell...
Potential improvements I decided against:
You could go Xeon, but the support isn't there for games, better off with the 990X.
You could go for a Professional grade sound card, but I think the X-Fi is better in games, and I don't like the idea of having 2 sound cards.
You could go to 3-way or quad SLI, but that simply doesn't work in enough games to be worthwhile. In the games it does work in, it's often slower than 2-way. Even 2-way is a little crappy to be honest.
You could add more HDs or more SSDs but I think any more storage is a little silly. Better off with an external NAS with RAID mirroring etc if you really need more than 5tb (!)