Pi Man - thanks! Some good race times you got there - nice work. I was also thinking about doing some faster/shorter stuff over the summer but I have just got to get a sub-3 marathon out of my system so I'm going to give Chester a go instead.
BM - sorry, just read back and found your earlier post where you said that! If you've been regularly running 70+km then it sounds like you're in the right place to start the P&D 55-70mi schedule. Best of luck!
If all goes to plan, I will be starting the same P&D schedule the week before you, targetting Chester.
BM - If you have been consistently running 20+ miles at 4:29km (7:13mi) then you're probably in sub-3 shape! But yes, that is too fast for the P&D schedule. The LT and MP runs will help with maintaining race pace, long runs are all about building endurance and promoting fat burning.
I am hardly an expert after one marathon, but during my race, I never felt like I was close to running out of energy. I believe it was the long runs that gave me that essential endurance by adapting to burn a higher % of fat at a given pace.