Re: sprockets & speedometers.
As far as I know, there aren't any 11T sprocket options for the HT engines (I have heard that making the engine drive sprocket much bigger would cause interference under he sprocket cover)....
An 11T drive sprocket is available from SBP BUT it is for use with their Shifter Kit....Maybe this is what you saw or read about?
As far as changing the gearing for higher top speeds you could get a smaller rear sprocket.
Hope this helps you.