I do this somewhat often. When you add in the trip to the airport, waiting for the plane, picking up bags at baggage claim etc, its often pretty comparable or you're only saving 1 or 2 hours. And with planes you deal with delays, luggage issues, etc.
My best tip is to leave really early if possible. Like 4am. Shower the night before, pack the car, and then when you wake up, just make coffee and go. You don't even realize what's happening until 2 hours later and you start waking up and feeling good around 4 hours. Then it's halfway done.