most speedo's are within 5% by adr specifications, but very few are actually that close...
i was in my mate's e32 750i the other day and what read like 240-250 felt more like 200ish.
and, OT, that things a bit of a darkhorse! goes from 100-200 quicker than it goes from 0-100!! hehe aaah 12cylinders.
one day when i'm filthy rich, i'm gonna have someone make me a rb52qetttt hehehehe