This is what I have found to work best for all round use. It works for any tire on any street motorcycle.
Look for the max PSI figure stamped in the sidewall. For normal running the minimum inflation pressure should be within 10% of this on the rear. The front minimum should be within 10% of the rear. This means that if you have a 42# tire the minimum PSI will be 38# rear (10% of max), and 34# front (10% of the rear). This will give the best overall handling, wet of dry, with good wear characteristics. Lower pressures will give a somewhat smoother ride, but at the expense of some wear and handling.
For extended runs, particularly with heavier loads or high sustained speeds, go to max PSI front and rear. The tire will run cooler because of less squirming. This will give better wear than a hot tire will. The difference in contact patch is negligible unless the tire is grossly under-inflated.