There are quite a few great local location to film mountain biking near Boston. In Milford, Ma there is "Vietnam", this area has a great mix of jumps, drops, chutes and techincal single track. The slow motion would look very cool capturing the compression of the full suspensions bikes and their riders. Imagine the image of a rider launching off a 8 -9 ' drop and landing on a 6" travel full suspension bike; Or a rider and bike compressing and absorbing 1-2' rocks as a rider pedals through a "rock garden"

For even more extreme action there is Highland Moutain Bike Park in NH, about 1.5 hrs from Boston. This is an old ski area re-purposed specically for mountain biking. Check out the many youtube videos, type in the highland mountain bike park. These helmet cam videos give no since of perspective. These are truly scary drops in person. With the high speed and HD, you could capture the rider as they soar through the air over a table top jump or ride out of the woods and drop 12' to the earth and bank into a berm.

The conbination of gravity, terrain and the impressive amount of abuse these full suspension bikes can take will make an excellent show