Matt you cannot expect a 10 year old car with XXX miles to perform like a new one. Exhaust blow may have an effect, to check if there is a leak, block the end of the exhaust for a brief time and you will soon see / hear any exhaust leak. Also you have no idea how accurate your speedo is, odds on it will over read. Taking into account the speed limit in this country you could check it out on a airfield or go to Germany and cross check your speedo against a SATNAV!
The other factor that will effect top speed is the wheel and tyre size (smaller rolling radius will reduce top speed) check wheel and tye size are same as the original fitted to the car
Maurice
July 2009