I now have 4 track days and about 800 street miles on the Kuhmos and they are almost half gone (4-5mm remaining of the 7.8mm original depth). This seems to be pretty reasonable wear for the performance they provide.
Because my stock suspension doesn’t have enough negative camber, it causes some extra wear on the outer shoulder of the front tires. Rotating fronts and rears only prolongs the inevitable. While at Miller I also experienced a little chunking on the middle of the outside front tire. This is typically caused by overheating. It was warm there and there are a number of corners that really loads the outside front tire.
Scott is running Nitto NT01s on his 3600 Lb, 400+ HP BMW 335i and recently got 9 track days from his first set. That is really good wear -- on par with what I will get from my Kuhmos. Oh, he’s like 17 seconds a lap (at Miller) faster than me too.
Replacing the Kuhmos with Nittos seems a no-brainer, however there is one more twist. Nitto doesn’t make the NT01 in the 245/40-17 size I use, they do however offer it in a 255/40-17. This is a little wider and a little taller than the Kuhmos. Luckily this is a very small amount and it should fit without any mods. Worst case a 5mm spacer up front.