In the Define Mini it's really cramped but I think that in a R3 you can actually use two rads, 50mm rad on the cpu and another 25 or 50mm rad on the bottom fan mount. That or maybe mount one of those really slim rads on the top with two Scythe slim fans. I'm guessing that in some setups it could actually work.
I was also thinking of dropping custom water cooling and going solely with ready-made solutions like the Kuhler 620. Currently I have one cooling my CPU. It seems that in the passing months Asetek (oem for Antec/Corsair/Intel) has put a kit for cooling a gtx 570/580. It's the same pump and 120/25mm rad but the pipes mount a bit differently to the pump. That should probably work on the Define R3 AND might work on the mini as well. You won't get super cold temps but it'll be enough and with right fans you'll get great performance and silence.
They also have this which looks great!
You can throw a dual slim PWM fans on that 50mm rad and there you go!Edited by adi518 - 7/10/12 at 8:18pm