I won't say much about the timing of your connection, other than the checked baggage delays at Dulles are even worse than I remember, and there may be a spot of traffic when the bus hits 66.

If you want to stick close to the metro at Rosslyn, either the Heavy Seas Alehouse or Kanpai (Japanese) are about a block uphill (on Oak). If you have the time to venture a bit further, you can sample some of the best Mexican food in the area (seriously):

Guajillo (on Wilson) is a sit-down place with good mole, strong margaritas, though a bit pricey (but takes credit card).

My favorite place is a bit of a walk (14th and Quinn/Queen), the taco truck El Chilango. Cash only, but top quality, and at less than $3 per taco, grab as many as you can handle!