All roads that lead to and from beacon are horrible for cycling.

That aside, I suggest riding route 301, which starts in cold spring and ends in Mahopac. It is 22 miles one way, but you can always turn around at any point. It's a great road if you like hills, no turns, good shoulders and mild traffic.

I urge you to just go riding for yourself and explore the area. There's nothing like seeing for yourself.