We have one with our club, Mike. I've had him codrive my cars before and its always a struggle to not be in the dust.
Miata, he tends to be 3-4 tenths faster than me.
Mustang, years ago when I was really in sync with it. we would run about equal times. That being said, he was equaling my times just hopping into it.
Mustang, now... he waxed me by a half second in the AM, drove something else in the afternoon and I felt lucky to close the gap to 3 tenths.
Of course, he got a jacket in the last year of G-stock, trophied in G-street (he was in a Celica, the Fords had an advantage from what I gathered) This year, B-street
We have another guy who is just off his pace, but you can tell he is working hard for it.
Mike... It takes little to no apparent effort. He will hop in, first run will be really fast, second run he cleans up the early parts of the course a little (dropping only a little), and maybe a third run to fix small details for that last sub-tenth. And this will be in a car he has never driven before.
For instance, I recently moved and met my neighbor at an autocross I was organizing (yeah, it was a "that car looks familar" and talk to him and discover that we live across the street from one another). He has a LS1 FD RX7 with coilovers and all that. Just a beginner autocrosser though, he went to a test and tune and had Mike try his car to see what was in it. BAM, 2-3 runs and set an almost FTD with it, observing that FTD would have easily happened, but the RE71R's were overheating. (Hugely faster than the car's owner, but moreso, car he had never driven before and right out of the gates a precise run within hundredths of FTD)
I aspire to cleanly beat him sometime.