I think your workouts shouldn't be exactly at your marathon pace. I normally do some quality workouts up to 13 miles, but the pace varies from slower than M pace to 10K pace. You never know what your real M pace could be in the race, so it is good to train a bit faster than your expected goal pace in my opinion.
I think you should definitely be on for hitting your target time. Typically in my build-up I run 10-14miles MP in a heavy training week and believe me this is a hard session, a proper mental workout as much as physical.
I know other people might do 16miles MP but this would leave me too drained and they are lower mileage guys.