Hi koiboy. You should find my 4:00 pacing chart somewhere on last year's thread. I expect I'll dig it back out at some point. Can't really help with you getting to 4:00 shape before then, though! Keep up regular 18+ mile runs, at target pace +45s (so about 9:50) but finishing strongly at target pace for the last 2 or 3 miles, every fortnight or so.
You're welcome. I have done a few ultras, sometimes on consecutive weekends but I try to avoid that if I can. The first weekend's long race - and I'd put M v H in that category - takes more out of you than you might realise. Personally I would do no running in between at all but fair play for doing a speed session. You must have recovered well.
Others might disagree and say it would be good to do short, low-intensity 'recovery runs' in between.
It's more a mind thing. Some might feel they need to go out to feel more prepared or they're frightened of losing fitness.