I'm interested, there are 2 of us doing the Hell of the Ashdown in Febuary in Retrobike colours, may I be as bold as to suggest http://www.cycleisland.co.uk/
on May 6th. I have also had a idea to do a 'Hell of the South' ride for a few years mixed Tarmac and track in a Paris Roubaix style.
Good stuff would be great to read a write up afterwards.
I think I actually prefer road bikes. However, on the road I think the differences in fitness would show more and perhaps be more of an issue? I speak as an old fat man so am more than willing to be proved wrong!
A nice loop with bailout options would be great though.
I agree about the differences in speed being more evident on the road although at the Herefordshire Road Ride in 2010 and 2011 we didn't have any difficulty keeping a small group together.
Also agree about the bail out options - if we target a sportive or two there is typically a shorter route that can be taken if weather/fitness/bike requires.