You may want to check your throttle cable to see if is adjusted right. Sometimes you can get a little more out of the machine if you tighten the cablee up.

 

When my 98 SP was new, the max. top speed was 47 mph. After 700 miles it jumped to 54 mph. The first test when it was new was on a packed gravel road; the second after 700 miles was on pavement so this will account for some of the difference. The altitude on both tests was approx. 3000 feet above sea level. Power losses related to altitude are approx. 3% per thousand feet. Incidentally all speeds were verified with my GPS.
By the way I did run against a Griz and to my surprise SP was just a little bit faster on top speed 1 or 2 mph. The Griz was new and not broken in so that could account for being a little slower.