I am running BFG's R1s square 275/35-18s.
I have three track days on them and they are holding up quite well. I think they will deliver 6 days. Grip is stupendous. Shaved more than 3 seconds from a 2:04 lap time. WIll definitely get them again after they wear.
Pressures have to be kept between 38 & 41 psi for best grip. If they go above 41 they start getting a bit slippery.