Great write up thanks. I’m running my 6th marathon in 3 weeks time. 
Also interested to hear about your long runs, i’ve been adding doses of 5-10km at mp into my 20 milers, generally towards the start/middle, but seem to struggle towards the end of my run. Not as quick as you … training for 4.10/k mp and easy pace just under 5/km so averaging out about 4.40/k for long runs. They have come mid volume though, no real tapering. Again… great result, well done.