I run around 35. If I plan to be doing some hail-mary driving I will up it to around 40. Usually run the fronts about 2-3 PSI higher then the rears, so 40/38 for aggressive driving. That is for the ContProContacts that I have though. I have ran them at 45/42 before which helped the response of the car but it tended to skid more. Those tires are known to have a fairly soft sidewall for better ride comfort/noise so it was as I expected it. A true performance tire should have a relatively stiff sidewall which means you can run a lower PSI for better traction.
"Optimum" PSI is highly dependent upon the weight of the car, balance of the car, suspension, driving conditions, and type of tires. We might as well be debating oil as well since everyone will have an opinion. Certainly nothing wrong with what is on the door-jamb, but I would view it as a reference point. If the car feels a little loose or sloppy in corners or feels like it floats then try adding some PSI and see if it feels better for you. If the car feels great then just leave it alone unless you are getting uneven treadwear.
If the car feels like it's beating the hell out of you when you run over a pebble then maybe lower the PSI a little. It's all a trial-by-error crapshoot really.