Re:GTX 470 high idle temperature 77°C (171°F)
Well that explains your idle temps. The drivers keep the card in a higher power state when running dual monitors. One solution is to use MSI afterburner and use the default user fan profile. It sets the idle fan speed 50% and that will probably drop your idle temps by 15C. 90C under max load isn't bad. The stock fan profile allows that by default and the cards are rated for 105C.
EVGA X99 FTWK /i7 6850K 4.52ghz 1.35v
32GB Corsair Vengeance LPX 32GB DDR4 3200
GTX 980Ti w/GTX TITAN SC for PhysX
Samsung 850Pro 256GB SSD/2x WD RE4Black 2TB
Corsair H100i V2/Corsair AX1200/Window 10 Pro