Gaming puts varying loads on your CPU and GPU making overall assessments difficult. You more assuredly assess the situation by running standardized load tests. In this manner the performance can be compared to other system's performance under the same standardized loadings.
Personally, I prefer OCCT's program as it includes both CPU and GPU loading programs. It also includes built in temperature and voltage monitoring, alarm sounds, recording and graphing of results over the test period and auto termination of the test if temps exceed preset limits.http://www.ocbase.com/perestroika_en/index.php?Download
I set my OC's to be < 80 on the GPU's and < 75 on the CPU when under full load using these utilities.
1. It's a safe bet that nothing I'm ever going to run will ever approach these loads.
2. It gives me a baseline as to whether I'm getting all I can outta my set up by being able to compare my temps "apples and apples" versus against other similar setups.
I used to run Prime95 overnight as my final test but after getting to the point that the 20th "final test" was not, failing, showing me anything to worry about or forcing me to turn down my OC's, I stopped bothering.