Our bikes have a fairly flat torque curve from around 2500 rpm all the way to redline, so shift whenever you feel like it. Or downshift whenever you feel it.
If you're looking for horsepower, it's above 5,000 rpm so rev the snot out of it for acceleration.
But seriously, where to shift is more of a matter of your riding style so there's no pat answer. When I'm just going for a leisurely cruise with my wife, I shift a lot sooner and just lope along. When I'm riding solo and hitting the twisties hard on the mountain, I run it up. So just shift according to your wants and needs. These bikes are bulletproof, and as long as you're not lugging the motor the bike will take whatever you give it. I've been riding mine this way for 44,000 miles.
