If you're cooling your CPU with air and only using a single GPU, I can't see any reason why a Kraken G10 wouldn't fit although it'd be easier to put the radiator on the rear 120mm imo. (edit - just saw you said in SLI - nevermind!)
You kinda inspired me actually as I'm running a GTX 780 SLI build now and while the temps are fine, I have to run the fans at 100% in demanding games and benchmarks to keep the temps under 80, so if I can get the temps just as low or lower while keeping the noise down, that'd be amazing.
So I've been looking into putting an AIO water cooler on my top GPU and the Kraken G10 won't fit unfortunately as it's wider than a dual slot GPU (should be fine if you're using a single GPU though). So, I think my plan is to get a bracket from keplerdynamics.com to mount a Corsair H55 to the card. I've seen pics in the [Official] NVIDIA GPU Mod Club - AKA "The Mod"
thread where people have fitted the Corsair H55 in SLI setups with no space between the cards and there's been just enough room for the tubing to get out, and also seen a pic of a reference GTX 780 with the heatsink removed, Corsair pump installed but with the stock fan still installed so hopefully the VRM temps will be decent.
So, I think it's feasible I can mod the card and get it to fit, but there could still be some problems.. I think I'd have to run the radiator fan at the back of the case as exhaust as otherwise, it's going to be pulling in hot air from the second graphics card below it, straight into where the CPU cooler is trying to blow air out. However, running it as an exhaust means a lot of the hot air from the CPU is going to be going through the radiator (a fair bit gets pulled out by the 180mm exhaust above).
So, I'm wondering whether the temps will actually improve much if the radiator is just being fed warm air from the CPU. My CPU temps are pretty good so the air won't be crazy hot but does anyone have any experience of this? Would I be likely to see an improvement?
I'll probably make a post in the "The Mod" thread later too to see if they have any ideas.
(posting at work so can't actually see if that pic works, hopefully it's ok!)