Oops. There are different MT Sporstman tires. One is SR, the other ST, the ST is mud and snow treaded.
There is a tire shop I found called Performance Plus that has some brands I've never heard of HP400 and Maxxis.
The reason I put 18s on my 944 Turbo and 928 is tire choice. The tests for acceleration, cornering, and braking were the same for 17 vs 18 even though typically increasing the rim sizes decrease all of those because 18s were better tires that you can not get in 17.
Those wheels are a really popular wheel style now. Can even get a set in 22s for the Cayenne that look just like em. My 22s are a little different spoke pattern that make a bit more center.
I really liked the Carrera Lightweights I put the the black 944 turbo. The were about the lightest 18 I could find.
They are different than the Carrera IIIs I put on the 928. The Lightweights were a risk for getting bent on the heavier 928.
Since I put these on the 928 a LOT of other 928 guys have put them on theirs, copy cats.