Subject to debate. 50c seems high to me with no load.My 1080 classy averages 38c to 42c with kboost on and no load but never goes above 61c under full load but would need more info to answer System specs and air temp of environment   Some people think heating and cooling are bad for the cards. i have a friend that leaves his gaming rig on all the time with kboost on and in 5 years hes never had an issue. i prefer to turn mine off when not using. i would be more concerned about temps at full load then at at idle. you can always change fan curve for lower temperature. i see no advantage of having card turned up when not using just uses more power and increases temperature. i let the card determine when it needs higher clock speeds Just my two cents 

My gtx 1060 stays at no more than 50c full load gaming. 50% fan speed

Yeah the gtx 1060 is a fine card, the cooling on it is good. The 5870 always ran warm but its been very reliable, it is a gigabyte 5870 super overclock, so it has a decent cooler it is just a power hog. The gtx 1060 is much more powerful.