Im z800 owner.. no such problem happen to my bike. Only the problem with the horn.. but after they set the horn, its ok already..

U must understand 2 different type of engine.. z800 is 4 inline which hs high HP. But kawasaki increase the size of the back sprocket so the torque of the bike increase.
Bcos of the 4inline engine, this bike quite heavy.

While monster if im not mistaken using vtwin engine which have good torque. And the bike is much more lighter than z800. But believe me, 4 inline engine is good at high speed compare to vtwin engine.

Try both bike first.