There's good and bad things about both the Enthoo Primo and the 900D.
I'd suggest taking a good long look at both and decide which serves your purposes better.
IMHO the 900D requires some modding to get to be nearly as functional of a watercooling rig and good looking of a case as the Enthoo Primo, but it does have a few advantages too. The Enthoo Primo blows it away in how easy it is to put in a nice custom loop with an overkill of raddage with little to no modding at all, but the 900D can be made to fit even more rads and is easier to deal with things like longer GPUs, etc. The Enthoo Primo blows it away in cable management & well-thought out design. The 900D's advantages tend to come not from it's design, but from the fact it's so much bigger.
Honestly, I would personally never even consider a 900D. If I wanted bigger and could fit more GPU & more rad, then I'd be looking at a caselabs case, not the 900D which imho is a generic Caselabs or 'Little Devil' wannabe. That, and the real deal-killer for me and the 900D is the terrible 5.25" bays. They are odd-sized (complaints abound from people whose 5.25" bay devices don't fit correctly, at least not without taking a dremel to them &/or the case) and the wider 5.25" bay covers (thanks to them being the full width of the wider-than-normal case) look terrible imho once removed so a 5.25" bay device can be put in. Every time I see that I can hardly believe Corsair did that. Why they didn't keep the brushed aluminum bay covers the width of the 5.25" bay so when removed it was still brushed aluminum on each side so everything could look flush and uniform is beyond me.
The Enthoo Primo, on the other hand, is so unique on it's own it can't really be compared to any other case currently out. It's design is so well thought out that it's almost functional beyond belief, and it's a work of art imho. It's not perfect though. I don't think there's a single one of us who owns the case that doesn't have a list of things we wish were changed/different about it. Then again, the same has always been true for every case ever made.
Edited by Unicr0nhunter - 12/26/13 at 4:52am