Most of the gamers only test the GPU through Furmark while buying, and if your cards are passing the stress test of Furmark, I think you're good to go. However, if you can somehow test the "GTA V (five)" (yes, the newer version of same old Grand Theft Auto) with highest possible resolution (of the game) in your system, it'll be the real test for your GPUs (especially of the cards till RX 200 series) in every possible way (stress, temperature, memory, etc). Play it for an hour, run to the Vespucci Beach (in the game of course), and see if everything's fine there.