In my very humble opinion it's not worth doing any rides over 75-80 miles in training – better off doing plenty 5-7 hour rides at a good pace. Big miles often equals a higher chance of injury.
Yesp, that'd be me.
R knee now in re-hab. Damn.
FWIW – I think something like 4 laps of Dalby's Red route will give you a taste of the kind of punishment you'll encounter. If you manage 4 without much trouble with a decent lap time, the MKielder 100 should be be manageable.
Last year I rode a HT, this year a full sus' since it simply makes life a little easier on the body.