The Richmond Park 3-Lap Challenge

But how much faster would a you be in a group - let's assume that everyone in the group is the same level, and could knock out a 1 hour time. 5 minutes faster? More? Less?

IMO

I think that you could easily shave off 10-20% as part of a 4+ group.
You only need one person at the front pulling while the 3 others are chilling at the back.
3/4 minutes turns and you're golden - your 3 laps / hour melts down to 50 minutes.

IMO