I ride two bikes at the moment, a Habanero ti road bike that takes nothing wider than a 25mm tire, and a Gunnar crosshairs CX bike which handles at least 40mm. For the latter I have two wheel sets, one with wide knobbies for gravel rides and races, and a set of “road” wheels. With 28mm slicks, the Gravel bike is barely slower than the ti road bike, which, I think is mostly because it is heavier. The gearing is slightly different however- road bike = 48/32 x 11-32, whereas the cross bike is 38 x 10-42.
I’m in southern Loudoun, South Riding/Stone Ridge area. You may need to drive west a bit until you find some gravel roads. Seems like west of Rt15 is where most of the gravel is between Loudoun, Northern PWC, and Fauquier. I tend to ride out from Aldie but you could easily ride out from Haymarket can connect in to the gravel.