I'm running Win7 with GUIminer,-w 128 -v.I'm running 11.5 drivers & 5/21/2011 GUIminer.For some reason the newer versions of GUI reduce mh/s.
I can get 375-390 mh/s,BUT my temp hits 85c,so I crank em down to get 70c-75c
BTW kick the fan to 100%,you'll need it
It took some OC'in.I'm a gamer & gamer PC builder,so it was just like tweakin for a big match.
It might be your OS.I have no clue about Ubuntu,my software skills suck