Usually, engine wear increases dramatically in the last 500-1000rpm before red line. I would stay out of those, but anything before that is fair game, as long as you warm your engine up first. I cannot stress this point enough, do not run your engine hard before its been warmed up. Start your bike before putting on your gear.
The rule of thumb with 600's is to always keep the needle in the upper 3'rd of the tach. So for real performance, dont let the needle drop below 10k. I cant seem to find a hp chart for your bike, but if you have one post it up and I'll tell you for sure. Here is the rough way of calculating the powerband.
1. Find a HP to rpm chart.
2. Find the peak HP on the chart
3. Draw a vertical line from the peak down.
4. Make a point roughly 70% up the height of this line.
5. Draw a horizontal line from this point, and stretch it lower into the rpm range, untill it intersects the hp curve.
6. where your line intersects the HP cure, draw another vertical line going down. Whatever RPM that happens to fall on is the start of your powerband.