Sensible,
Running frequent 20M runs @ ~MP often has the consequence of 'blowing up' shortly after the 20 mile mark. You're actually working too hard for your body to make optimum adaptions to the aerobic conditioning - the main one being the ability to burn a high proportion of fat which you'll need to do to race 26.2 miles. Also by going a minute per mile slower, you'll be on your feet for ~20 minutes longer giving an additional 20 minutes of effective training.
I recall Mike Gratton previously posting that his long runs were around 6 min mile pace - and he ran his marathon at sub 5's!
I'd suggest slowing the long runs down to >7 min miles to start, maybe speeding up a little on the second half, but no fsater than 6:40ish for now.
Make sure you get in a long run of 2 - 2.5hrs (you may need to build to this by adding 10mins per week if you're not already there) and a second one of 90mins - but remember to cut back slightly every 3rd or 4th week, depending how you feel.
Keep up something a bit faster during the week - mile reps at ~32min 10km pace, but don't worry about any feeling of lost speed in your legs. Paula R's 3000m time improved with marathon training, which shows the importance of a solid aerobic base for even middle distance events.
Best of luck with your target - get the first one out of the way and I'm sure you'll be running 2:25 before long!