With the stock cooler neither runs cool.
Under Prime95 the Q9300 with a stock cooler hits 70°C just like the Q6600.
The Q9300s 7.5x multiplier limits you to 3.6GHz (7.5x480MHz) if you're very lucky. If you're not it hits the FSB wall before that.
With a good cooler the Q6600 can go just as high.