(Updated 9/22/2020)

Ben Nephew posted the route:

Whitehall and Upton State Parks in Eastern Massachusets have some of best singletrack in the region. I mapped out a route combining the trails in both parks that is about 20 miles, which is a long loop considering the average trail length in the area. The trails are not hilly, but they are winding to say the least.

Ben Nephew posted the route:

This is a 22 mile out and back on one of the most difficult sections of trail in New England. If the entire 114 mile Metacomet Monadnock trail is too long, but the 12 mile 7 Sisters trail race is too short, then you can connect sections 7 and 8 of the MM for a challenging 22 mile.

amcberkshire.org/mm-trail/guide

John Spinney posted the route, with a Strava segment to track the FKT.

While this is a short test it packs quite a punch. I'm not sure it even counts as something worthy of an FKT but I'm going to share this. Last wknd i ran hard up the steeper more technical side of the Pinnacle in Stowe, VT. Since not everyone uses strava i'd love to know what others have put up. The link is below. This is from the Stowe pinnacle parking lot. From the meadows parking lot i think sub 20 minutes is doable as the first half is not as technical and more runnable.

Ben Nephew posted the route:

The Pachaug Trail runs 24 miles from Green Fall Pond to route 138 in Griswold, CT. It is part of the CT Blue Blazed trail system, and is mostly singletrack with some jeep roads and a few short road crossings. Starting at Green Fall Pond, I ran the trail in 3:46:18 on 1/19/15.

www.ctwoodlands.org/bluetrailsmap

connect.garmin.com/activity/678084940

This route links up 4 huts in Maine's Carrabassett Valley region.  These are the Grand Falls Hut, the Flagstaff Hut, the Poplar Hut and the Stratton Brook Hut.  The point-to-point route following the main trail from West Forks to Carrabasset Valley is 47.3 miles.

Brent Sitterly posted a VK route (below).  But, this route starts at Pleasant Valley Road and is ~ 3500' vertical in 4.8 miles.

So I've been obsessed with the vertical kilometer event.  Apparently there are at least two peak in Vermont that could support such an effort, Killington and Mansfield.  I am going to attempt the only route I could find on Mansfield that will have 1000m of ascent.

Route:  1.7-ish miles down Mountain road from Underhill state park, up Eagle cut to the Laura Cowles trail.
Total vert:  ~1000m
Total horiz:  ~4.5 miles