when you look at the chart there really isn't that much in it. Most of the people that ride these sorts of bikes would never use the top end of the rev range, only the middle section,(most of the time). All of the bikes there are very close to each other. To get a guage of the USABILITY of the horsepower you need to look at the whole graph, not just the peak. A flatter line will equal more usable power, and the line with a rapid climb will prov very difficult for the average rider to harness the power and use it affectively.
the other thing you need to look at is the torque that each engine produces and at what revs