Last week I went to watch one. Today I have registered. Looking at the photos and statistics, I will be the fattest, the slowest and the beetroot-est runner, but I will have a go. The slowest runner last week came in at 41ish minutes, and I ran 40ish minutes at the weekend - but this was on flat, known tarmac and the Darley course is on grass, hills and goodness knows what else! However, I will go along in the comfortable expectation of coming last and that way if it's anything different I will have exceeded expectations! At the one I went to watch, they assured me that they always wait for the last runner and they've never lost anyone yet
There is one caveat though - it it's raining I won't go, because I have two work trips abroad in the next few weeks and I cannot risk slipping and injuring myself. So fingers crossed for good weather, please!