Carbloader: Lots of good advice has already been given, but I'll add my tuppence worth.
If you are running 40mpw you are not incurring the same amount of fatigue in your legs that someone running 60/70mpw, hence you will be able to do your miles at a faster pace and still find it "easy". Your two cycling sessions a week will also help your aerobic side without punishing your running legs. That is the good side.
The bad side is that you aren't getting as many impact miles into those legs and not developing the endurance side as much. A seven mile run is just over a quarter the distance of the marathon.
Your 10 miler @ 6:45 pace is good and you state that you try to break up your harder running sessions with road or mtb cycling sessions, it might be that if your hard running sessions are three/four days apart then you are actually doing a mini taper for them and running them at your peak on fresh legs. This will give you fast times and a great feeling but might not be the most appropriate training for the day of the marathon.
To run well in the final quarter of the marathon you need to get the impact miles into your legs through long runs and medium long runs, you also need to learn restraint and hold yourself back in the early miles when it all seems so easy.
Decisions on what is MP on race day should be made no more than a couple of weeks out, current training should be based on current performance, preferably from a recent race.
There is more than one way to run a marathon you just have to find what is suitable for you.
RFJ: Sounds like life getting in the way again.
KR: good luck with the XC.
Gul: How's the 10K training going? are you following a specific program or just doing general running and seeing how it goes?
Ant: I too have been reading Julian Goater's book, interesting read. Have found it very helpful, not your normal running book.
Jools: Congrats on the new PB, is that a course PB or an all time 5K?
TR: Yet more sound advice, you should try to get a writing job with one of the fitness mags, they may even be prepared to pay you more than a few matches.
Lorenzo: Another decent run, miles in the bank.
Martin: 18 without fuel or fluid, do you do that distance with sustainance often?
Birch: 12 miles slow is still a decent run, any bad reaction to it?
Blisters: Will be interesting to hear how you get on. How many words meaning pain do you know?
Minni: Congrats on the first 20, how many 20s are you planning and will any more be unfueled?
Parkrun for me today 19:10 or there abouts, was slow to switch of the watch. Too busy getting breath back after last hundred metres sprint. No speed back yet but getting stronger.