It might be totally different on closed roads, though I've watched a video of Box Hill on RL, and it looked distinctly less pleasant than anytime I have driven on it.
The time I finished my first 400km (around 250 miles) I was greeted by the organiser while he was cleaning up. He said "You're 10 minutes late, you've missed the cutoff ..... just kidding, made it with 10 minutes to spare". I had cycled - mostly alone - from the edge of london to the edge of Wales and back again in 27 hours. Maybe my ego is strong, but I didn't need a bunch of cheering strangers.
Anyway
@172traindriver has experienced the cheering crowds. He should try it without and tell us the differences.