For Ascent, I taper 7 days because I walk about 10 of the 13 miles. My finish time was 4:09 last year and I live in Kansas. This year I am doing the marathon, so I will taper about 10-12 days, again due to walking during the race. My weekley miles ranges from 20-35 per week throughout the year.
In response to:
Not sure if you're asking for the PP Ascent or Marathon. I'd say two weeks or just a bit more for the Ascent, and more like three weeks for the Marathon. But I'm also interested in hearing what others have to say.