ya know - i have been doing a lot of reading on the slip ons and the PCIII and when you translate from cars to bikes its a whole different story -biff is actually right - these bikes do come pretty lean from the factory and the whole exhaust system is so short to begin with that even though the slip on might seem like a minor add on, its actually apretty big difference on the motor - and with the O2 sensor yes, the bike will make up for the difference to an extent...but whats the point?, you buy an 07 CBR - put the extra loot up and do the sh*t proper.

so, a must have? kinda stupid not to.