Yeah, I've done it in awful conditions (98 for any long term HONCers) when you had to pedal just to keep going downhill and I did that on summer type tyres which make the road stuff fast. It just isn't technical enough to get any benefit from mud tyres.
I'll be on a CX bike - did it on a CX bike for the first time last year and enjoyed it approx 179% more than previous ones - the road/bridleway/non-technical stuff feels really quick and the more technical stuff ( which feels really easy on an mtb ) is much more fun 
