I did the opposite of a planned GAP tour ride. I waited for very good weather, got a motel within driving distance of a trailhead, and did two long out-and-back day rides. The weather was perfect, and the rides were very nice with just a camera and a jacket stowed in a handlebar bag. B&Bs and other accomdations near the trail need advance reservations, but motels farther away are easy to book.

The crushed stone trail surface was mostly very smooth and hard, with a thin coating of peppercorn sized stone fragments, and very occasionally looser surfaces. I was still significantly slower than on a paved road.

Day1: 66 miles. park at Rockwood, ride uphill to the Maryland border, the Mason-Dixon monument, then back to the car. Head west on a second out-and-back to the Pinkerton Tunnel, and also ride it's detour path.
A lightweight gravel bike and smooth 38 mm tires were perfect for this. I averaged close to 12 mph uphill and 15-16 mph downhill, even though the grades were very shallow.

Day2: 56 miles, park at Connelsville, then uphill all the way to Confluence and return. Passed through Ohiopyle in the middle. The grade is often about 0.5%, so the speed difference each way was only a mph or so.

Both days were great. I often had no other riders in sight, except near trailheads and near Ohiopyle. The out-and-back was fine, with different views and different times of day as I retraced my route.