Confused...
Agree, we're just using different terminology. I use smooth for how an engine runs and peaky or linear to describe acceleration. Anyone that's ever ridden a two stroke knows what peaky is like. The throttle is like a light switch, it's either on or it's off, and you better be hanging on if it's on! Supersport 600s tend to be peaky as well, you have to rev them. I'd say linear describes your Z, my CBF and the parallel twin Ninja's. There's just a nice linear (smooth) rush of acceleration, no big power hits or OH sh!t moments.
A linear (smooth) bike is a lot easier for a beginner to learn on because it doesn't have that big surprise of a power surge that will loop it, surge forward uncontrollably etc. That's one reason I got rid of the BMW R1200, even though it's typically not thought of as a peaky bike, it has lots of torque, but you have to rev the boxers to keep them in the happy zone. Basically you had to keep it between 6-8000rpm if you were riding aggressively so you ended up riding it like a supersport 600. I really prefer the linear nature of the power on the CBF (or your Z), they just pull from anywhere, shifting is purely optional. ;-)
I guess I am totally confused now...
When we talk about a smooth ride is different then when we talk about a smooth speed rush...
High end Inline 4 bikes not only have smoother engines, but also have better chassy component which produce an overall smoother ride. Even if you just set the bike on neutral and coast down a hill, you will find that coasting is a lot smoother on higher end bikes then with entry level bikes.
Now the smooth linear power that I think you guys are talking about, also has to do with things like fuel distribution design, higher end bikes with sophisticated fuel injection have very predictable take off and power rush, while entry level bikes tend to have more simpler carbs or fuel injection systems that produce a more jerky results when you twist the throter.
Also, the jerky behavior can be due to engine design trade mark, twin engines tend to be very jerky even in the way they IDLE and they also tend to have an early rush of power but also an early peak for this reason I don't think Twin engines are good for beginners, but every entry bike now seems to have a twin engine on it.
Inline 4 tend to be a lot smoother, lazy at the begining with a rush of power in the end (higher revs). I would said that a Inline 4 500cc bike with such a smooth behavious would be ideal for a beginner instead of a jerky twin.
I think the smoothness of an engine from while at idle to when at higher revs is different then the smoothness in power delivery and the smoothness of high chassy component in general...
The problem with a beginner riding a bike like an R6 for example is the endless amount of power, the more you step on the gas the more it will go and if you don't have the skill to be riding at higher speed and you don't know how to control yourself, that is where the problem is, but other then that, a bike like a R6 has a very domesticated and predictable power delievery that is very smooth and friendly instead of Jerky and peaky as found on some of the wild twin engines...
I don't know if I am making any sense... just how I see it...