I grew up in the area, haven't been back in about 7-8 years, but Route 6 would probably not be a good option. It is not a highway but is a pretty fastly-driven road multi-lane road with shopping centers, etc..., especially towards mattapoisett, fairhaven, etc.... If you ride up by Rochester, Lakeville, Acushnet, and maybe Middleboro the ride might be better. I never did anything like a 5 hour ride back then, mostly 1 hour or so. But good country riding (although it supposedly has changed dramatically since I was last there). Try www.baystatetriteam.com, probably more feedback there. Good luck!