What about idel temps?
Are there any reference sites for this? I can't seem to find any.
If 77c is under 50% load alraedy, what would if we assume that the GPU load is under 100%?
What is the safe max temputure?
To avoid flickering on the 2nd monitor, they will not idle as low as normal. You can expect about a 15C increase in temperatures as a result.
A 680 will normally run about 80C under full load, but you are safe up to 100C. (I would not let it go beyond 85C, regardless). If it gets near that range, you can adjust the fan profile and get the temps lower or fix air flow issues.