The good thing about the H70 is that you can isolate the environment of the radiator. By that I mean dunk it into a cooler of ice water(no fans), or have it hang outside of the window in -30 canadian winter(with fans). 5ghz anyone?
The fluid wont freeze inside the h70. Ethylene glycol is antifreeze. I have been meaning to contact Corsair about the percentage of antifreeze in the loop however...
I wonder how cold it has to be to start freezing :3