I have averaged about 55 MTB miles a week for the past 13 weeks. I have dropped bout 23-25lbs.
But dont let mileage alone be your goal. As you get better on the bike the flatwoods ride will become just a training ride. I did 19 miles at Boyette today and got twice the workout 18 miles at Flatwoods would give me. Flatwoods is more of an aerobic workout where Boyette throws in the anarobic aspect during some of the bigger climb outs.
If you keep riding 70 miles a week you will be riding Boyette/Alafia by the end of the month!
Good luck, I may see you Tuesday night.