The Quadro K5000 is the same as a Geforce GTX680, except that it has been unlocked and optimized for the workstation, it carries a different memory system, but the core configuration is the same.
Thus we can expect the same limitations of the GTX680 to be in place. The GTX680 has a maximum temperature of 95C, but for longevity I would recommend around 80C being the highest it should be allowed to go.