50c is fine. Generally, as long as the temps stay under 60c full load, you should be okay. Once it goes beyond that, then your asking for trouble. I believe the AMD TBirds are rated to operate at temps up to 70c, but you wouldn't want to take your chip to the melting point. Also, a lot of probes measurements are a little on the low side, so 50c could actually be closer to 55 or 60c. If possible, you might want to hook up an intake fan, preferably in the lower front part of your case (if you don't have one already). I noticed all you mentioned was the 80mm exhaust fan. Also, if you aren't using a good thermal compound, like Arctic Silver, that might be a cost effective way of dropping a few c's off your temps too.