I have a SISU 22 with a cabin. I put lifting rails on last spring, IE not molded. I have a 4s Johnson 115 with a 4 blade prop. I can cruise at 18Knots and WOT is 26 Knots. I think the 90 will feel a bit under powered IMHO.
i 2nd,the idea of using a 115 instead of a 90hp,i have a 115 hp yamaha ,4 stroke on mine.its just about right. i think if you go on the even keel web site ,they suggest a 130 to 150 hp for a cabin sisu.