I can't tell you. I have been running 55 for about a year and I haven't encountered any problem's. Mine are rated 35 max. Choose your own course. Personally I'm thinking about trying 65, just to see if their is any further improvement.
Well, so far as I can determine, it does. It seemed to me like I didn't start seeing that noticable an improvement, until I got to 50 psi. However, I was impressed enough, when I went to 55, that I quit fiddling with it and I never really went back to try to document it.
As far as a rougher ride, it does give a more harsh ride. That's the primary reason that I'm only doing it on the car I am driving, so's I don't get no grief.
As far as tire wear, I think that if anything the tires are lasting longer than normal. As far as abnormal wear, the only thing I've seen is when I got down to the last 1/32, then I could see that the middle was wearing slightly faster than the sides. Since it was well past the short side, as far as rain and stuff, I really figured it was begging the question, at that point.
I run 50 psi in mine like I posted before but about the rougher handling: I really don't notice a rougher ride, buit what I do notice is that it almost gives you a feeling of power steering because the contact surface is smaller. I have also not noticed anything out of the normal as far as going around corners and such goes.
Tire wear: it's too early to tell yet. I have driven like 3000 miles with these tires and sofar don't see abnormal wear patterns.
Mine say 44 max, and I run at 40. If I were you I wouldn't go much above that 35. Of course a decent tire will usually take much more that whats its rated for. If the tire explodes, it was too much. It also depends on your driving, and mostly the condition of the roads you have to drive on. Crappy roads and really high pressure doesn't sound like a good combo to me. Lots of highway driving would probably allow you to go higher. I was told by a friend ,he used to race auto cross, that newer tires tread wear is not affected as much as older tires were by pressure changes. And they changed pressure all the time, but usually in the other direction. So what I did was to look at my recommended pressure 29, which was with 35psi max tires. and when I got 44 psi max tires, I figured they were made for more PSI, so I added 9 psi (difference between new and old tires MAX pressure) to the recommended 29 psi and ran them 1 psi lower than that BEFORE I started driving for max FE. Wich if I havent confused you with my math, was 37 PSI. Once I started driving for FE, I went to a conserative 3 psi above that 40 PSI and havend has any problems so far with tires that are near the end of thier service life anyways. As always, YMMV!!