I recognise a great deal in what you say. My one DNF met three of your crisis conditions (and I'm still convinced I would have been in danger had I carried on). But at last year's Sussex Stride I went into an aid station determined to drop because I wasn't having fun. Only carried on because the aid station crew were so bloody lovely to me as I sat taking up space and sulking, and I couldn't think of a good enough excuse.
Am particularly interested on what you say on the difference in predictability of a 50 and a 100, as I tentatively plan to step up to the latter.
Have you read James Adam's blog on this? Good stuff.
Screamapillar, that's what worries me as much as anything. The actual races will get rolled over to next year, then the next year, then the next, with them keeping most of the money raised for "expenses" before they've actually accrued any, and no audit trail to show where any of it went.
Of course, I might be wrong. They might have it in a ring-fenced account with full documentation, with the interest going to the charity. And their share declared as income on their tax return. Maybe.