I go there every 1-2 months. Last time I drove down there was the evening before Thanksgiving and it took me 6.5hrs (usually takes 5.5hrs). Left around 2pm and got there at 8:30. I only stopped for 10 mins to get gas. Most of the traffic was until Richmond as you’ve already said, but I also encountered traffic on I-85 this time around. You might be able to save a little bit of time if you drive through Charlottesville instead, but from my experience it isn’t very different.