I have finally filled up all my ports with ONLY U1's and U2's and have had a lot of instability and often returns back to the company with U2's vs. U1's. I've had to return 5/13 U2's and not a single one of my 21 U1's.

Since my supplier was so nice as to not to make me ship them back and simply take my word for it, I've got a handful of heatsinks to put on some U1's that don't get as much fan coverage as the others. They almost all run at 2.0 whether they're a 1 or a 2, anything more, apart from a few running 2.1, and i just get huge loads of hardware errors.

Just thought I'd throw my experiences in here.