could be wrong, but you can get your engine to have loads of top end speed or decent acceleration but not both, just a happy medium... I know with motocross by changing the pipe etc you could have top end or bottom end power, or just meet in the middle... I was going to remove my cat but the torque loss means acceleration suffers for the sake of top speed (how often do you really need that?!)
I know a guy whos just got a CTR and he says its wild acceleration but poor top end, to have the speedo reading out nearly 160mph must have amassive degree of error in it surely? I think the only way to check it out is with GPS, nobodys speedo is accurate thats why the plod allow a few % when you get caught, depends on the size of your wheels, aswell - thatll send your speedo way out.