My 1080 rarely exceeds 65°C on full load, but that rack has enough fans to takeoff on full speed :p
From all the tests i did over the years on several cases, i've always found that pushing cool air in was way more efficient than drawing warm air out (aka positive pressure in the case).
If yours is a bit limited in fan mounting possibilities, maybe it's worth looking for a new case in the long run. Those graphics cards tax the power supplies a lot more too, so these too tend to get warm, all in all, new computers run hot.
(For the curious, it's a 3U rack case that is too shallow to be closed because of the 1080, but i mounted a 3U fan plate atop in the front side with 3 Noctua 12cm fans tamed by a fan controller that pushes air into the case, effectively cooling the PSU and 1080. Two 80mm fans are mounted in front of the SSDs and RAM/chipset heatsinks, again, tamed by the fan controller. Lots of fan but no noise.)