Stress Testing Your Mac For Optimal Performance?
There is a built-in hardware test designed by Apple.

With the introduction of Intel-based Macs, Apple has built the AHT utility right into your Mac. 

Simply hold down the D key while starting up your Mac to boot into the Apple Hardware Test.

I would not recommend using garden variety www not approved test programs. This would be the same as if you have a car with a speedometer marked 150 MPH would you actually drive it @155 MPH to find out if it holds up using non OEM tires?