Recently, I started to get frustrated toward my Greater Calling performance.
I use Greater Calling as previously stated: (when needed)
  • push for progress
  • push for Quality

Greater Calling is perfectly skill to push for progress. 3 turns of rapid synth 100% going to success. That results increase progress without losing durability. So, this skill will be better than Piece by Piece/By the book. (The reason is it's a flexble skill that you can allocate steps such as 2 for progress and one for quality.)
However, in the situation of difficult synth, 3 turns of careful synth usually returns very depressing results on quality improvement. Usually, it's barely success, so the quality is increase by 10-20, while the durability still lose as usual. That is not good. Even a failed careful synth might do the same quality improvement.

I should really use Bold Endeavor... (when it get fixed) :P
but ya... I can't find any other solution for it...