I've cycled in the vicinity of the roads you've picked, though I'm not sure how much of that precise route I've ridden. Anyway, Hunterdon County (where Frenchtown and Round Valley Reservoir are located) is an excellent location for cycling. If you just stay off the main highways (such as Route 22), you should be very happy with your selection. My wife and I sometimes drive up there, park our car, unload our bikes, and just choose roads from the county map. We've never been disappointed, though a few unpaved roads were rough on our road bikes. If your bike is suitable for the occasional gravel roads, then you can hardly go wrong in that area.

Ken