I'm running two reference 290's at 400h/s at 1030/1250 -100mv core -100mv aux 0 power level. Fans are now at 50-55% at 85C, this is inside of a Corsair 750D.
I need to put a kill-a-watt on it but it's made a significant difference on the temp with only a 20h/s loss. That's the highest core I can get to at the moment, stable.
Stock BIOS, should I load in the 390 STILT's bios?
One of TheStilt bios for the R9 290 should let you kick the temps down quite a bit while still bumping the clocks up some.
On ETH I'm routinely seeing 80C more or less at 1100/1250 under LINUX though I'm running the fans a bit higher than you are.