Indicated...also actually it was in km/h, which can be a bit more off than mp/h.

What would make you say that? There's exactly the same speedo error for mph as well as kph. It goes through the excact same sensor and jost multiples kph by a constant to get mph.

ps. Top speed of the S2000 (or any other car) depends mostly on the stepness of the downhill (up uphill) that you're driving on as well as the amount ot tail/head wind. I'm sure that you could find a steep enough hill where the S2000 will top out at the end of 4th gear (or earlier), let alone 125mph.