well, I've never actually raced my Prarie with my Z, but I have raced Prarie Vs. EX many times, and the Prarie was right up with the EX, and the EX isn't much behind a Z, so it would hang, especially for a 600+ pound utility
No I haven't, but I have got to think that an aftermarket exhaust, jetting, and a freer flowing airfilter (although '03 stock filter better than '02), would have to add another 2 - 4 hp at least! I don't know of anyone who has actually dyno'ed one after doing any modifications to the engine.
I also removed the shim and now have a squel while I am ideling. It goes away when I put it in neutral. This week I am going to put in the smallest shim they have. My belt is a little too tight at present.
The black spring is from Erlandson Performance, it is like a clutch kit. I have the red/black springs in mine with 28" 589s. I lost 2 mph on top end after the tires and springs. That was checked with GPS and not the speedo. As far as acceleration, I have not lost much at all, I can still walk away from my friends 660 grizz.