Is Pen y Fan from Storey Arms really the best route for an MDC run? There's one obvious route that's a bit too short for the faster people, with no obvious "nice" extension short of going half way up Fan Fawr, and there's no significant short cuts for the slower - given PyF is the objective, just going back down from Corn Du won't be popular, nor that much of a time saving. Suggest that if the main route option was clearly longer then slower people would have been more willing to cut short - 5.5 miles sounds too achievable!
Needless to say, I don't get why Pen y Fan has had such a pull this time; we've far more exciting, longer, hillier, runs - with better priced and more convenient pubs after. Surely main benefit of Pen y Fan is the views - and you aren't going to see much in the dark...
My suggestion would be that everyone runs at their own pace and, when the faster people find themselves ahead of the group behind them, they loopback, collecting up others as they go, until they get to the slowest person at back of the group at which time they turn around and continue in a forwards direction until they find themselves well ahead of the group again... and repeat. That way everyone gets to run at their own pace, nobody has to stand and wait for the slower runners, the slower runners don't feel that they are holding people up and the faster (more able?) people get to run further than the slower folk. If every runner takes responsibility for the person behind them, nobody gets left behind.
Pennine start off in a big group for about a mile or so then split depending on what people fancy and the groups that have formed naturally. Headcount for each group once they split.
This is how I group ShUOC runs as well.
The problem is that the two particularly slow runners have no insight into their slowness and even when groups spilt they will still opt for the faster group. I froze last night even when I was wearing 3 layers on my top half. I think ppl need to be made more responsible for their route finding, know where there going and not expect to be led round making everyone else freeze in the process. That way they can cut off short of needed.
We were talking about a system like that Elle, which would probably work, but makes for a less enjoyable and very convoluted run for the faster people. Ideally we'd have several groups, but as Clare says, some always want to be in the group that's going the furthest. Then there is also the issue that if the group splits then there needs to be a responsible leader in each group (who knows where to go - and we're talking about fell runners here...)
As for Pen y Fan, it's always going to be popular as it's the biggest hill in the area. Yes it's a dull route but it's much more interesting in the dark and usually turns out to be quite a notable run.
If there really are people that slow that still insist on going with the quick group then you have to split naturally by going fast then regrouping with fast people only and splitting before the slow people have a chance to catch up. This of course has to be organised as the leader of the slow group needs to be known beforehand and able to do a mid group pace. So you regroup to them then split while they take care of forming the slower group ideally with someone else responsible bringing up the rear with the slow ones.