I have the same boat that had a 150 Merc on it. i was running a 25 Trophy. I just put a new 200 EFI Merc and moved up to a 26 Trophy. I will probably back down to the 25 once the water gets in the 80s. I am around 5600 first thing in the morning and then she dies down to 5300 during the heat of the day. Hope this helps.Brian