The big bore kit includes a forged piston, better rings, and if you have them do the work, a better bore job than you get from Kawasaki. The result is less vibration, zero oil consumption, and improved torque and horsepower. The improvement is 4 to 5 horsepower.Price for the 685 kit is about $325. Piston has a coated skirt. Wrist pin is also coated.
The stage II head (also available from Schnitz Racing) includes porting and slightly oversize valves. It's beautiful work. Combined with the 685 and some light carb jetting you can get 43 RWHP. The bike just runs stronger everywhere. It's about a 9 to 10 HP increase over the stock bike.
No financial interest, just a very happy customer.
all the best,