Nate, you weren't kidding when you said the flow decreases greatly at sub-zero. Here's some testing with just a 6' loop out and back in. Pump is a RIO rated at 1,090 gph!
At room temp
This was about -27C
The interesting thing was I let the chiller get down to -30C, then turned the pump on, and my temps decreased to about -22C over about a minutes time. It then took about 10 min to get back up to -29. I don't know if that means anything or not, or whether with two gpu's and a cpu will decrease it even more. Gonna test for condensation on a GPU tonight.
I don't know if I should use my HK 3.0...didn't someone say not to...rubber o-ring or something.
I just need a cpu block now.....