Up to about 4000 RPM they are very much like standard pipes but once you hit 4000 RPM it starts to come on the pipe and from then to the redline it just keeps pulling, and you still get the massive hit of power and torque around the 6000 mark.
Having said that the power delivery feels a bit more linear than the standard system - that's the impression I get anyway.
They dont come cheap - they are about the same cost as a reproduction set of standard pipes, but I wanted something different and the JL pipes were recommended, they are also very light and fit really well.
When I bought the bike it was fitted with a set of tatty standard pipes hence why they had to be rpelaced.
Only had to go up 1 size in main jets to take full advantage.
I think the ones on the GPZ are Higgspeed pipes which (having had a set on my old KH500) tend to be a bit more peaky - guess I'll find out how well they perform when I get it going.