Interesting questions from Jack, and I wouldn't quibble with the responses.
I flew with a skipper who was 75% a few months back, he said he's working harder 75% than he was full time 6 years ago!
In my experience that sounds very credible.
The current work load is not sustainable full time in my opinion
Judging by the numbers trying to get onto one of the part time contracts you are not alone in that belief. The ability to sustain the full time workload is becoming a major concern for many, in both seats.