What temperature is 50-60? The mobo, the CPU, the GPU?
While 50-60 C is not critical it is a bit warm. I wouldn't be over concerned on an objective basis, but I'd never accept in any of my builds. Unless I am maxing out in stress tests I want my mobo below 40 C, my CPU below 45 C and my GPUs under 55 C.
The GPU temp is fine then. My GTX 470s are rated to do 115 C (although I've never allowed it to climb above 100 C). Nvidia publishes specs on temps and I think that the GTX 660 is rated to do at least 100 C.