So is it possible to get around 30 MH/s with system alive?
Try
-T max-temperature option:
bitcoint-miner -T 50 .......
Then the miner will decrease speed if Videocard temperature is higher 50 Celsius degrees.
nice, didnt know that feature exists.
you should add it to -h (help)

EDIT: i actually see its already implemented, but not always displayed.