Yep, I'm in the exact same boat. We don't have nearly as big of a farm as you operation, but out of almost 100 GPUs, the only ones we have had issues with have been Gigabyte "Windforce" models.... the coolers are not very good at cooling and the fans die much faster then any other models we have.  In fact, in the past <18 months all of our cooler/fan failures have been from them except one Asus Strix 480 that has a sticky fan (one out of 3 fans on it, so it still cools very well).