Welcome.
Regarding the speedo - has it got one of these fitted (a small gearbox that sits on the speedo cable)
https://www.wemoto.com/parts/picture/hl-454000
Not sure why it would only affect speed reading and not distance though.
Top speed? Haven't tried, I think the "S" was road tested to about 125mph?
I've not come across a restricted SV - on the EFI models they use a different ECU, on the carb models they blank off part of the inlet port. You might be able to spot it if you remove the airbox and open primary and secondary butterflies and peer inside.
https://www.youtube.com/watch?v=iQetbr9bU5c