navigation system is an accessory which is offered in most new cars of reasonable standing but is usefull only in countries where GPS is avaiable and digital maps of all roads of the country / region(like europe) are fed into the navigation system memory.
i think top speed is usually written in the manual and if it electronically limited it is also mentioned. just for clarification some people here think that max of the speedometer is the max speed. please understand that speedometer is a common part and same part is used in many cars just by changing the upper writing or the needle, the mechanism or electrical parts are the same so if a car has meter of 200 or 220 its not its top speed.