I had an '05 Busa, and really couldn't find fault with the engine.
Mine was stock except for the Akrapovic full system, and dyno'd at 160 HP at rear wheel.
But most pleasing was the torque and fuel injection.
Suzuki has their FI nailed. Only had one hickup with the FI and it was my fault (well the idiot in front of me actually).
At 3000 RPM it had 80 ft/lbs of torque which grew to 94 ft/lbs at 4500 PRM and maintained all the way to redline.
Because of the torque, it was a breeze to ride. You could put it in 6th gear and putt at any speed above 40 MPH.
At 80 MPH it got 45 MPG and 41 MPG at 90 MPH.
At the opposite end of the spectrum, at 140 MPH, the engine is now into the power band and is ready to rock.
As for the HP claim, all that takes is an overbore and some cams.
Yoshimura did it for the X1 Busa endurance racer, which put out 196 HP at the rear wheel.
It's too bad that Suzuki didn't go the way of the Yoshimura X1.
I think even more Busas would have been sold.