I guess it all depends on what part of the Potomac you want to fish. Nice Bridge (301) and below I would really prefer at least 18' boat like your former Parker, and a 20' one is not a bad idea if you get caught when tide and wind are opposite or one of the quick summer storms blows over. I do recall a fair number of larger Carolina skiffs out there on decent days, not sure if the aluminum jon boats are less salt friendly, or just a lack of real dealer support in VA/MD for them (other than BPS).