Cinebench R20, and it really depends on whether you're using stock cooling, if it's an open case or not, and the temperature outside. Stock cooler, closed case in a tempered room should yield around 50°C with moderate browsing after a few hours. At full, sustained load, as long as you don't go too far over 80°C, then it's normal. Over 90°C though, there's a problem.
It also depends on your video card/GPU : if it gets very hot, it will raise temperature in your case - you should keep an eye on temperatures while gaming. If you use an open case though, Cinebench R20 should do the trick.