I come across a few newegg reviews for the cougars regarding them buggering up when placed horizontal. But not everyone mentions it (I guess not everyone uses it horizontally, either...) so I'm wondering if those ones just so happen to be quasi-defective? Because those same users usually report that when used vertically, they run fine.I would stay away from slipstreams for a radiator fan. I got 3 of them just to mess with and they don't have good static pressure. They move a lot of air but they are also noticeably louder then my other fans on full speed.
Check out the cougars, I keep hearing good things about them.