We used to take the 81-66-17-95-4 route all the time, hitting 95 at Fredericksburg, VA about 1 hr south of Washington. It seems that over the last 10 years or so, 95 south of Washington has become extremely busy until you get south of Richmond. There have been many times that we have been delayed in this area.
We have tried an alternate route from northern PA and then heading to Washington and hitting 95 there. Tried that once and will never do it again. We hit the Washington area around 1:00 AM and it was still crazy busy!!
Our preferred route now is to take I81 all the way to southern Virginia and then I77-I26 and meeting up with I95 in South Carolina. This route has a lot less traffic (especially tractor trailers) and is much more scenic. You do cut through the Blue Ridge Moutains at one point, so that may be a factor for some.