I have been using a gtx 660 for over an year and half now... Previously I had a simple zebronics cabinet with no airflow and temps were 50-55C idle and 80C at load... Then I switched to a cooler master elite cabinet which allowed me to add intake and exhaust fans... Then the temps dropped drastically...
As of now I have 1 X 120mm intake and 3 X 120mm exhaust fans (all of them are 90cfm and directly connected to psu) so they run at max rpm always and the temps I see are 34C idle and 72C on load...
So to summarize, better cabinet and airflow helps a lot in cooling... And nowadays within 2-2.5k you get very decent cabinets...
As long as the max temps you see are not above 85-90C, there is no problem... But idle temps around 50-55 will make the room in which the computer is located a lot warmer, its good in winter though..
Also fans at 90% when the temps reach 70C is not a problem too... you can tune it using msi afterburner and create a fan profile... but there will be a lot of noise...