How hot is too hot?

0: GSA 10081029: BM1362:02T 42C 317mV 369MHz T:369 P:369 | 99.1% WU:100% | 325.8G / 373.3Gh/s WU:5215.2/m
1: GSA 10081028: BM1362:02T 42C 317mV 369MHz T:369 P:369 | 94.3% WU: 97% | 391.2G / 366.0Gh/s WU:5112.8/m

Looks like I'm running about 42C. I have the small fans attached and a larger fan blowing on them.