If you are training for a marathon I would build distance, then speed. As you increase mileage you will slow down, but then the pace will come back naturally as the body gets used to the distance.
As a general rule, most people do their slow runs too quickly, and quick runs too slowly.
I would follow your marathon plan as closely as you can. Back off the distance for a while if you experience knee pain. When you have a decent mileage base then do one session a week (tempo or intervals) at eyeballs out, but the rest at a steady / easy pace.
I would absolutely love to see a velodrome-style 'elimination' running race where the last placed runner is eliminated every lap of the track. 25 participants starting with the winner running 10k total - would be awesome but brutal.
I won the Dartmoor vale marathon a couple of years ago (v small race with about 150 runners)
What was very surreal was being led by the guide vehicle, a large 4x4 driving 20m ahead of me at all times. I was completely alone for most of the race (won by 20 minutes in the end) apart from this truck.