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.
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