If you are mining in a room with an air conditioner then I wouldn't worry ever about them overheating. Especially with only 5 GPUs. You need to consider the fact that gamers pretty much ABUSE their gpus and nothing happens, that's what the thermal shutdown programmed in the bios is for. If any GPU goes over a certain temp like 100C, there is a signal sent to the motherboard and it sends a shutdown to the computer. They do this because even if a GPU is idling, its possible a fan can die and it'll eventually reach a huge temperature and need to be shutdown.
Gamers keep their GPUs inside an enclosed case usually with poor cooling and they OVERCLOCK their GPUs. And what is worse they usually have SLI type setup where one GPU barely gets any air circulation and the GPUs are fine. They are built to handle extreme heat in those situations. So you shouldn't worry about your open air rig with an AC in the room.
It’s weird my board just rebooted when I was reading ur comment !… it’s a server board, it’s got its issues!….