Well, a group of us found out this Sunday. After completing the Duffy Lake road, we checked the map in Cache Creek and decided to loop north to Clinton, and come back down to Pavilion via the 81. The map was not detailed enough to show surface, but one of us was fairly sure the road was paved. The road from Clinton to Kelly Lake was great, twisty, and no traffic. At Kelly Lake however, the paving ended. It was a long way back through Clinton and down to Cache Creek, so we decided to head down the dirt road and see how it went. The bikes (FZ6, VFR and BMW1200GT) behaved amazingly well, even over severe washboards and steep rutted inclines. The 15 km road took us over a huge mountain, and many sections were one-vehicle width with totally blinds corners, so speeds were generally 10-20 km/h, although we did get up to 80 in some stretches.
We all grew up riding dirt bikes, so I would not recommend this rides to newbs, but it was a great learning experience and adds to things that amaze me about the capabilities of modern sport-bikes.
Needed a 200 km/h wind to blow the dust off once we hit the paved road