we've done it a few times, but not for quite a while. Last time we did it was about 6 or 7 years ago, when we were younger

& had no kids. It's not bad if you have a few drivers, but if it's just 2 people driving, it's pretty brutal. We usually leave around 3 or 4 am from Hamilton, ON. If you get tired, stop. My DH actually fell asleep driving in Georgia 13 years ago (thank GOD I was awake & noticed) & we had to pull over at a rest stop to snooze because sleeping in the car is not like sleeping in a bed. We worked nights at the time so we were used to being awake all night, but we couldn't handle it & we were 21 at the time too. We pulled over & slept for 4 hours in the car & then started driving again. For the $$$ to spend on a hotel for the night, we've found it's worth it. & if you do drive thru without sleeping, by the time you get to your destination, you're exhausted. I would never drive straight thru with young children. I couldn't imagine being in the car with kids who haven't slept properly & cranky & crying. Teenagers I can see being able to handle it, but not young kids. We always drove down when I was a kid, but we always stopped for the night & the last time we drove down we stopped in one of the Carolinas for the night but on the way back we drove straight thru with 4 drivers in an Intrepid & it wasn't the greatest ride but we managed, again we didn't have kids at the time.
We always get the trip ticks from CAA & go their route thru Niagara Falls, thru Pennsylvania, the Virginias, Carolinas, Georgia right into Florida.
Don't forget you will have to take weather into consideration as well. March is iffy. We drove home in an ice storm thru the mountains & it wasn't pretty one year.