Nope, the speedo runs off the front wheel so gearing changes dont affect it.
They often read funny at the upper end of the speed range though.
I dont think the ST4 is that much more, the ST4S is becasue they are generally newer bikes. My 1999 ST4 was about £3200 when i got it two years ago.
Glad you like the bike though!
[Edited on 11-11-2004 by rockhopper]