Riverside Dr could be faster. I use a road bike with 23s in good weather and don't find many places that require me to slow down on the Greenway early in the morning between 158th and 96th Streets. I don't know how to connect to the Greenway at 72nd Street. Mostly I just prefer to stay away from motor vehicle traffic. Before the Greenway was completed I used to come down a section of Riverside Drive and was uncomfortable with the relatively high speed traffic well above the posted 30 MPH especially in the sections with narrow roadway and parked cars. You should try both to see which you prefer.

Perhaps you should consider crossing the RFK bridge. I have seen a few cyclists on it, just not sure how to connect from Manhattan's streets. I also understand that the bridge walkway has signs to walk your bike and that the railing is extremely low to the point of being dangerous. But, you probably could come down St Nicholas and across somewhere to the 125 Street entrance. You end up on the roadways of Randalls Island and then get back on the bridge walkway for the crossing to Queens.

Have you seen this bike map of NYC:

http://www.nycbikemaps.com/maps/nyc-bike-map/

And this about the RFK:

http://www.astoriabike.com/2008/03/t...provement.html