Tmoth I'm a P&D convert & certainly don't have natural speed. I would say endurance is more important than speed for the marathon, the threshold & MP sessions are they ones in P&D, the VO2 max stuff is more for sharpening & making MP feel easier.
I don't think a marathon campaign is the time to be working on your speed if it's an area of weakness, how much is it going to improve over 12-18 weeks? Unless of course you're really going for it on the speed sessions, but if you're working that hard on pure speed then it's going to mean your missing out on working on another trait more important to marathon success. It's part of the reason I only do the one marathon a year, I like to dedicate the summer to shorter stuff & do more regular speed sessions then, hopefully that then benefits the next marathon campagin
TT - I think I'm another with a definite endurance bias, I know a few local runners who would beat me over 5-10k but once we get to a half marathon then the tables turn. I will have a look at the schedule & what follows the week after to see if it's worth saving the legs. There is a 20 mile race on my doorstep that day, possibly worth doing that as a training run with some at MP.
TT - Interesting thoughts on the long runs, in my previous two campaigns I've gone no longer than 22-23m & negative split both marathons. I've stepped up to P7D 70-85 this time & this has me doing a long run of 24 miles. I think that would probably take me longer than my target marathon time, maybe over the top then?