I've driven multiple 1ms on track. Standard wheel/tire configuration, standard wheels with 275 rears, standard with 295 rears and 18x10s running 275s (or maybe it was 265s) all around. I was absolutely shocked by the difference the square setup made. The 1m has always felt a little bit twitchy to me at the limits and also hard to perfectly balance. It's a great car but not real comfortable sitting right at 9/10ths. With the square setup that totally changed. It became extremely predictable and progressive. It went from a car that I drove around the track and somewhat reacted to when things happened to a car that I could attack the next corner with. For me, it went from another street car that’s occasionally fun to take out on track to a car I can’t wait to get on track again.
Granted everyone’s driving style is different and opinions will vary. This is just mine