I wouldn't push past 85 degrees if I'm honest.
Overclocked mine to 3.4GHz and it was hitting 90 under load (35 idle) so dropped it back down to 3.3GHz. If you think your cooler may be limiting the overclock then I suggest investing in another one, it can make all the difference!
Pay attention to your Northbridge as well, they get very hot and cause instability past a certain threshold.