At this stage it's looking like the option. So much to see coming down from NY to DC. Philly & Baltimore on the way looks like a good way to break up the trip. Just for perspectives sake, out closest other city from Adelaide is Melbourne which is a 9 hour drive away (South Australia to Victoria) which we South Aussies regularly do, so 4 1/5 hours from NY to DC is nothing.

Just have to remember to stop getting in the passenger side of your cars when I want to drive!