I would carry it all on from Dulles. At the Frankfurt Airport you can store your luggage while you go exploring; there are "left luggage" facilities in Terminal 1 and 2: http://www.airportcity-frankfurt.com...26.storage.htm

Two weeks ago LH let me board with my 22" rollaboard and a good-sized tote bag (to my amazement) - FCO-FRA. You might have to check the bag from FRA, but at least you'll know where it is at that point.