I would probably go that way (295/penn)- that's how I typically get to 50 to head to the beach. (I live in Arlington, work in DC.) If leaving from DC, I typically take MD Ave through Capitol Hill to 50, but I think the other way would be faster from VA.
also, if you can leave by 2:00 and then kill time (coffee, drink, whatever) once you get into Annapolis, you'll probably be happier. that said, it's not summer so you might not have to worry about it.