Second monitor on iMac and heat generation

Hello everyone,

When I connect my Cintiq 21UX to my iMac 27" (2011) the GPU heat (Radeon 6970m) jumps from average 50C to average 70C while working in Photoshop. This is normal - the GPU heats more when in dual-monitor mode.

What concerns me is this: is it safe to constantly have the second monitor plugged in? Can the constant increase in heat damage my iMac after a prolonged period of time or are they designed to work under what is, in fact, constant load (I read something that running two monitors is like never letting the GPU go idle).