[jonathan180iq]

Out of the box, the GZ can touch +/-80mph.

With proper tuning and favorable conditions, it can do just a little more. But not only it is restricted here by power, you're also looking at redline with the factory gearing. The 16T sprocket increases the gearing of the final drive, theoretically giving you room to go faster. But the limited power then cannot overcome the taller gear to use it. There have been some guys who spent a lot of time trying to increase power along with the higher gearing. What's the magical new top speed you ask? ......+/-80mph.

The bike is what it is.

I loved the 16T sprocket because it gave more around-town smoothness to the shifts and I think is just so pleasurable for back country roads. My max speed dropped down to around 75 or so but that still let me cruise on the interstates between different parts of town. What is 5 mph anyway when we're never really on the highway to begin with?

To answer your question, at your size, you should still push 70. More with a tail wind.