I guess I need more power to drag 'em!

Well unfortunately I never ran the boat with the blower motor in it before I installed the ext box, I installed it all at the same time, so I cant answer your question. I do know the boat handles much better with the box, just dont know if it scrubs any speed.
I'll be testing the 900 motor and different props in about a month so I'll see how it handles then.
When you say "you went backwards" do you mean with the handling or you lost speed?