My $.02 - It'd be worth the extra ticket cost to change flights and avoid the transfer. As noted, you'll hit rush hour into NYC ... not fun. The cab/car will probably end up costing even more than noted due to "wait time." If you're going to do this anyway, I'd go along with the previous posters who have suggested the train. Traffic can be really, really bad. I'd expect at least 2 hrs at that time of day.