In reply to Mattyk: I don't do the score classes (concentrate on doing very badly at A) and have probably only done a couple more MM than you so take this with a pinch of salt, but going off my general experience and discussion with my mates who regularly do the score classes:
get a thumb compass a la orienteer and learn to use it on the hoof - this quickens up nav a lot (I did this and am a convert)
the string thing works if you know your own performance well AND it is calibrated to the terrain - lots of people were fecked by this last year! Someone I know who has 20+ years MM experience and has won the Elite did really badly on day 1 LS because of this - maybe practice on last year's course or at least Howgills / Cheviots as the terrain is not dissimilar
don't worry about what performance is required - work out what you can definitely do and just go very hard at that (and don't be late obviously)- such thoughts would have been very counter-productive last year, the people who did well realised quickly that a conservative unambitious approach was needed
good luck! wish I was doing it P