Hi Katie:
To add to Dave's reply and address the question about pace, the B ride pace is on the lower end when the climbing is at the 1000'/10 miles rate.
In the 'Area Wide "B" Rides' description (under "Interests" on this website) the range provided is 14-18mph while the 'Asheville "B" Paced Weekday Rides' quotes 12-18mph and the 'Mellow Burners' references 12-15mph. All of them say the lower end of the speed range is for the more challenging terrain. The lower rate of the 'Mellow Burners' is likely because those are longer 50+ mile rides.
Regards,
-Robert