CLEVO P870TMG-1 GTX 1080: Best way to test/stress GPU for errors?

So I've finally made my mind on selling this thing. That's why I want to know whats the best way to test the GPUs (GTX 1080 x2) for any error. What is the best software and configuration.

I've tried Furmark 1440p + 75C temp limit (Asus GPU tweak) for a few minutes and didn't see any problem, but I'm not sure if that's the best way to do it.

I usually play Guild Wars 2 and Apex Legends and haven't noticed any problem on them neither, but I don't know if that is enough to say they're good to go.

 

3DMark Fire Strike and Time Spy, in stress test mode, IMO. I own the Advanced Edition, but I'm not sure if the free version has stress test mode. Otherwise, you could loop Unigine Superposition.

 

Is it ok if I limit the temp to 75c during the stress test or should I remove the limit?, It can get pretty hot

 

You should remove the limit when stress testing.

 

I tried both and everything looks fine, but it was the benchmark mode, not the stress mode since I don't have it. I will also run Furmark and OCCT for a few minutes.

 

3dmark vantage at 4k on loop can be pretty brutal too.