Maybe your PSU not enough juice or maybe PSU is failing?

i had the "original" EVGA 1080 FTW. had no problems, the card chewed through things like Arkham City (which was an unoptimized mess) and Witcher 3 with ease. G-Sync is amazing on this card.
 
i did get the thermal pad upgrade just because i could. i did see some throttling issues, but only in benchmarking utilities (Unigine Heaven mainly). i eventually did the iCX upgrade.
 
which brings me to my next question: why aren't you looking at the FTW2? the first 1080 FTW probably had the normal defective items percentage rate, so you shouldn't expect a problem. but the new FTW2 is out anyways, which addresses much of the cooling concerns. you might as well look at that instead if you're really worried.
 
EVGA customer service still remains the top compared to other vendors. at least if you're in the US anyways.