I was running 34/38 in my M3's but I'm a big guy ~115kg and they felt good MOST of the time, they got a bit squigly when pushed.
They also flattened out a lot. But that's a combo of commuting and being a big guy.
I was happy with the feel and the wear on the fronts so I went up just 1psi to ~35 and I upped the rear to 40. Much better, and no squigly feel even with my weight.
I can't notice a loss of traction with that 2psi change.
I've not tried 42, because I'm happy @ 40.
Ant