When I upgraded to 17s, I was told to run 4-6 lbs less than the tires maximum rating for best performance and handling. However, that didn't result in the best ride quality for every day driving. The key is to make sure the tires are wearing evenly. One old school way to do that is to paint stripes on the treads with white shoe polish as wear indicators and adjust the pressure as necessary.
My 17s are rated at 51 psi max. They do seem to handle better if I keep them between 40 and 45 psi but the ride quality definitely suffers. The ride is a lot better at 32 psi but I haven't done the shoe polish test yet to see how they are wearing. I'll probably end up compromising somewhere between 32 and 40.
DC