Gravel over pavement takes getting use to the squirm, throttle control is the most important to stay up. Slightly underinflated tires seem to help (I use 17.5/19 on my old t'wings)
If in NE Pa. or NW NJ, try National Park Rd. off of rt 611 in Delawre Water Gap. Beware gravel right at the turn in. After fun twisties, a wicked, blind decreasing-radius, you hit wide gravel over rock for 2 miles or so, heading to Totts Gap. It has enough turns and hills to stay interesting.