Agreed with hunter. 45 is safe, but of course it will heat up under load, and that's what matters. Figure out those temperatures and you can know if you're safe or not. Run Prime95 and HWMonitor. Prime95 is a stress test that will put you under maximum load, and after about 30 minutes you'll see the highest temperatures you'll reach, so you can watch those with HWMonitor. It's much better than playing a game for 4 hours and watching your temps, or playing and your computer suddenly shutting off.