I'm using 4.9.2 on my windows 7 x64 pc and it's running 2x U3 stable with these settings... in case it's a help to anyone.
Avg 115 gh/s.

cgminer.exe -o stratum+tcp://blah.blah.blah -u my.name --au3-freq 240 --au3-volt 790

(One would run fine on 775, the other needed more juice to work reliably. 800 caused zombie.)

I have each U3 on a separate motherboard-usb-hub (they're stacked 4 high, I have them in the 2nd and 4th holes).

YMMV.


Edit: Must be a dodgy U3, even after all the fiddling, it sits at about 30Gh/s. Whereas its friend is 65+.