I've been inching the hashrate on my Newpac slowly every couple days.  I'm at 450 MHz and getting ~93 Gh/s now.  My goal is either 100 GH/s stable or 600 MHz stable.
Active cooling, and directly powered by a 5V 60A power supply instead of USB's current limiting features.  (EDIT: Newpac has stock voltage set.)
At 400 MHz it was still slightly cooler than the 2pacs and Compac running at 200 MHz I have on the same setup.  Haven't checked at 450 MHz yet, as i just upped that today.

Edit:  seems like it doesn't like 450 MHz. - 400 MHz gave me ~90 Gh/s.  93 @ 450 isn't as good of a jump as i expected.  Upped it to 500 MHz but was getting 41 Gh/s.  getting stable ~98 Gh/s at 425 Mhz, so that's where i'll stay at for now until i can adjust the voltage setting (and confirm temps).