48-49C under load is fine. The temperature at which the CPU will crash depends on your overclock.
At the rated speed, it should work fine up to 70C (even up to 90C). But if it's overclocked 500Mhz, you could have a hard time keeping it stable at 55C. You'll just have to find out the hard way.
I have a 3.06 at 3.3 that runs at about 60-61C with no trouble. Of course, I wouldn't recommend running at that temperature (I just don't have much concern for the well being of this chip).