SO-CRATES,I take it Bill and Ted were a big influence,lol.I just got a pair of M4 GP style slip-ons. Online for $476 with free shipping!! Just Google "M4 Exhaust 2010 Z1000" They are trick looking - all black. Akropovic also has a pair of slip-ons, and while the craftsmanship appears awesome, I didnt like they way they looked on the bike (or the price, at almost twice that of the M4s).
M4 claims saves 9lbs and +3HP.
Its usually the catalytic converter thats the biggest bottle neck in any kind of stock exhaust system. You can blame emission regulations for that one.....i put 2 bros on my friends 2010. even with huge di inside the mufflers it is only slightly louder. that under frame catilitic converter is the main restriction not the stock mufflers.
I dont know anything about that exhaust in particular, but I can tell you that GPR makes other products, and the ones I have used have always been of high quality. I really liked their steering damper I used to have on my ZX7RR.Does anyone know anything about the GPR dual thunder exhaust. They look pretty sweet and well made. I saw them for sale on ebay.