how harmful is mining and how to know if GPU is ok?

[clem84]

Earlier this year I bought a few 280x and used them for mining. Now, they were used for approximately 2 and a half months before I stopped. I've heard that extended mining can be harmful for GPUs.

1- Now, is 2.5 months long enough to do any harm? They were running 24/7.

2- Is there a program out there to test the reliability of my GPUs?

I've downloaded a few programs to benchmark them (3Dmark, Unigine). Everything seems to be ok but these programs measure performance right? (fps, temperature, etc...) They won't tell me if my GPUs are fully functional. Or maybe it's the same thing I don't know. I want to sell them and before I do I want to make certain that they're 100% functional. Any advice?

[RodeoX]

I would think the best test is to just play a video game. Does everything look good? If so, I think your ok.

[notlist3d]

There is no official test.  If you ran for 2.5 months solid chances are they have been worked harder then traditional gamers card.   

Try playing games look for artifacts.   Look at fans make sure they are running ok.   If video output after a few hours of play time looks good fans are working good chances are your ok.

I would keep the original receipt in case they do crap out most do a while for RMA's. Some companies are better then others on timeframe.