I have a 20' harris with the 60 Big Foot. It runs about 20-22 on the GPS.
The 90 might go a bit faster but it is quite a bit heavier.
I got my engine fron an internet supplier (ITG Marine) and it worked out OK. I
did save about $900 with prop and shipping. Some of that was the tax I didn't
pay.
Just take it to your local dealer for the "hourlies" and they will kiss and
make up pretty fast after they get a few hundred in the register. Sales and
service are usually separate profit centers for the dealer.