4 1/2 is a great over/under and makes for a tough call for me. The determining factors are pretty much where/when would I have to drive, what is the expected level of traffic along the route, how "taxing" is the meeting/engagement expected to be, and what is the cost of the flight. If I could use the driving time in a more productive way, I would probably fly. If it's a marketing call and I don't expect the meeting to be much more than "meet and greet", then I might drive.

But, from the greater DC area, the airport choices make getting to a lot of places within a 4 1/2 hour window fairly easy. Driving from this area, on the other hand, can be a real pain and full of unexpected delays.