FD - thanks for the additions to the thread and I think it just shows how much there is to consider. I have a good understanding of much what you list and a working knowledge of the rest, I am still at the phase where I don't know it 'off the cuff' but know of it and where to research it/calculate it: to be honest, I like it that way in some respects - I will therefore never assume I know it without checking.
I was recently in a room full of industry bod's and it was amazing just how many did not get AST/FLEX and how it is safer (they felt it was less safe and would rather 'give it a bit more') - also agree that stop margin when using AST has little to do with real ASD, but it sits on the safe side so all is well in the world.
Clearly enough to keep me interested for all my working days!