I have a 290X that is between 70-80 C all year long. Been running well for 3 years now inside my desktop PC case. Obviously not the best situation and my open air cooled rigs are much better but I do what I can with what I have.

To cool your rigs better, you need to exhaust the hot air. It won't be pretty, but something like a box fan above each rig, blowing the hot air into a dryer vent hose that you can run to the outside somehow, like up into your kitchen and into the exhaust fan.

The key to cooler rigs is exhausting heat! The heat generated will almost always overwhelm an AC or fan cooling system trying to blow cool air in. You need to take the hot air OUT so that it doesn't heat up the room and just get recycled over and over gradually increasing the GPU temps.