1.7 with a xp-90 with a good fan is what I will be pumping into my crappy clawhammer.
and O yah, 1.6 is very safe, I use 1.6 on a silent boost lol
and I forgot to mention I have been using it on the thermaltake silent boost with a 25cfm fan lol back in september, and only currently threw in a thermaltake smartfan 2 75cfm which I dont even run @ max speeds .