New Owner of a 03 Stratos 190F/S

Just picked it up on Friday...

It has a 150 Johnson, only had it on the water twice. Once on the Ohio on Friday (*hairy, passing trees and al kinds of good stuff) Took it out to the local lake today, seems to be real nice.

Any idea on what type of speed I should see? Speedo said about 55, and that was at about 5300RPM, prop is 21"pitch.

Still had a little left I think. (forgot my GPS)
Anyway if any fellow owners have some tips let me know...How many mph can you gain by going to a SS prop...