To put yet another different spin on this thread... I got round on four months road/mountain bike training (lots of long rides and hill work but no running at all) then just two months on the fells plus the taper.

The fell training was a long walk/run every weekend building up to 35 miles / 12,000' or so a bit faster than BG pace... this gave the "time on feet" aspect always throwing in as much steep ascent/descent as possible.

Meanwhile weeknight hill sessions on the bike, 2x20-minute threshold intervals on gym machines, hill reps up & down Glastonbury Tor... three of these sessions a week for climbing fitness without hammering my knees, the hill reps on the tor also gave some valuable extra descending though I never did more than six per session (300' per rep). You don't need a huge volume of this kind of work, quality counts.

I only hit the magic 10,000' /week a couple of times. Last big day out was the Welsh 3000s, after that two and a half weeks taper/recovery when I kept up the threshold work but didn't go on the fells.

The five miles into Keswick at the end of my round was my longest flat run all year... in fact more than the *total* flat mileage I did in training