I find this the most enjoyable race of the year! You set your own handicap so (if you're honest) you all finish at the same time. Or if the turkey's lying too heavy for some you can give them some encouragement as you pass them on the hills! Fantastic atmosphere, lots of fancy dress and hundreds of people saying 'why are we doing this?'! Go for it.
This is a great race. You give your estimated time at the beginning and start at different times. It was the first race I ever did a few years ago.
Being Boxing Day there are plenty of 'slow peeps' but I think they like to limit the estimated times to no more than an hour (10 minute miling) for the sake of organisation, otherwise fasties would be waiting for hours!