What type of system are we talking about here? Air cooled? Water cooled? High efficiency residential? What does the cooling load look like? The discharge superheat (and actual line temp) can vary quite a bit depending on the system load and effectiveness of the heat exchangers. What are you looking to do, heat reclaim? You may be able to calculate a number at design conditions but there again it's usually a small fraction of the operating hours. If you are doing heat reclaim the goal is to capture as much heat as you can, so one would select a heat exchanger with somewhat larger capacity than the compressor.
Probably going to run about the same as R-22. 120-180 like as been said too many variables.
I agree. Years ago, I was told by one of my mentors (who is long retired) that given all other things being constant (operating conditions, ambient conditions, efficiency, application, etc...), that when comparing different refrigerent systems (r11, r22, r12, etc...) the temperatures don't change, just the pressures those refrigerents operate at. I have found that to be very helpful.