The belts do take a few miles to bed in usually, at least mine always feel as if they do, after 50-100km or so mine feel ok.
The 2000 clutch springs may be ok to use, what scoot do you have?
It does sound like your new belt is longer if you gained 7mph on it. I used to run a 736mm belt when stock was 729mm, that gave me similair gains to what you got, thats why i think it may be a little longer on yours.