Sub 4 training - on track or not?

Brief history..don 2 marathons in last 10 months (Dublin and Paris) and finished both in 4.34. Currently training for third marathon in September (Berlin). Would like to do sub4 or at least close!
Previously I have concentrated on banging out the miles but his campaign I am including speedwork. My current schedule is as follows:
1) Long run - between from 10 and up to 24 miles run at between 9.30 and 10.00 pace.
2) Marathon pace run - 6 to 8 miles at betwee 8.45 and 9.00 pace.
3) 4 x 800m repeats. Normally run at around 7.20 pace but this week averaged at 7.08 pace (PB)
4) 12 - 20 back to back laps at the track (4.8 - 8.0 k). Try and runa s close as poss to 8.00 mile speed. Best 8k has been to date 8.11 pace and best 4.8 k (12 laps) is 7.58 mile speed (this morning!)
5) Weight training twice per week
6) One day complete rest.

By half-marathon pb is 1.58 and can reasonably comfortably run 10 miles at sub 9.00 min miles and have run 15 at this pace before.
Any suggestions for improvements or comments.
Many thanks.

For a moment I thought your were on about a sub 4 minute mile phew!
Your training plan is well structured but I would add/substitute a session such as this, one of my favourites and a great session if you can do it right.
Start off running 20 minutes at about mar. pace then 15 mins at 1/2 mar, 10 mins at 10K, 5 mins at 5K, 3 mins at 3K and 1 min at 1K. I know this sounds complex but all you really need to do is increase the pace at each juncture. This session helps with the speed endurance (the last 6-8 miles of the marathon) and if used regularly will give you increased speed over 10K. Usually i cover between 8.5 and 10 miles in this session but it can be quite painful but definitely worth it. Good luck with Berlin!

Thanks MG. Think I'll try this one replacing (2) above. Makes sense I think to do this on the track as I can work out a pacing schedule that mirrors this (and of course its alot easier to monitor every 400m). Thanks again.