I would go with a Spitfire X7 15″. Had a 2016 1775 pro guide, 90 hp, and put a 17″ X7 on, and gained about 4 mph, and about 300 rpm. But I also raised the engine one hole, to two open holes at the top. If I were to do it again, would go with a 15″ X7 and leave the engine at the stock height of one open hole on top. If I remember right, I was at 37-38 mph and 5350 rpm with the stock 17″ alum Spitfire, and 42 mph and about 5700 rpm with the 17″ X7 spitfire. I did pick up some steering torque from raising the engine, but never got around to adjusting the torque tab, to see if I could correct it, as I sold the boat to get some garage space back.Was a fantastic boat, and I miss it, but really didn’t need two boats. Posted my actual results on walleye central, search, muskyed. Sold the boat to a member on here, through this sites classifieds. Would have kept that boat forever if I had more garage space, but two boats, and two vehicles in a three car garage doesn’t work out well.