Depends on the situation, but I usually shift at about 3500-4500-rpm when riding around casually. For the 500, I wouldn't let the revs fall below 2500, and if you're accelerating quickly, maybe keep it above 3500. As Qken pointed out, lugging the motor is not a nice thing to do to your engine.
As rpm goes up, the oil pump naturally pumps faster. This is ideal because you ordinarily need more oil at higher engine loads. The only way you can throw a monkeywrench into the works is by being at a low-rpm and suddenly twisting the throttle really hard: a high-load / lower oil-pressure condition. Bad for crank bearings.
Don't be bashful about letting her rev. I used to think that my Superhawk would have a longer life because it made high torque at lower rpm and if each piston stroke automatically equals wear, then my Honda V-twin should last almost forever.
Well guess what happened?:
http://www.chrisandlisachan.com/superhawk.htm
The 500 was designed to rev, so let her. As long as you aren't stuck in traffic with a temp-gauge reaching red, it will actually be good for it.
Good luck.
-CCinC
P.S. If your owners manual says anything about this, DON'T BELIEVE IT! My Superhawk's manual was talking nonsense like I should be in 6th gear at 35-mph--must have been written to appease the EPA or something, because that bike would be at about 3200rpm at 65mph, so 35mph equals about 1723-rpm--"
ca-clunka-ca-klunka-ca-klunka."
