I have a similar situation...I'm thinking a whole-house type fan that would suck the warm air out of the bonus room and into the attic would work. If the door to the bonus room was open, the cooler air in the rest of the house would get sucked into the bonus room in theory.
I'll just echo that everyone's situation is different. For us, it's basically 80% deferred and 20% Roth. We will retire this year at 55/54 with good sized pensions (one is military) that will cover most/all daily expenses and put us towards the middle/top of the 22% bracket...we will see how...