Here are some of the differences as listed by Mercury:Mercury MarineIMPROVED DURABILITY AND RESPONSEOnly OptiMax Pro XS features Carbon Fiber Reeds to control airflow into the engine crankcase. Carbon fiber reeds produce improved performance and efficiency because they are more durable and responsive than stainless steel or other fiber materials.MORE HORSEPOWERThe Pro XS offers a Higher Wide-Open-Throttle RPM Operating Range, giving you more propeller options to maximize the performance of your boat.TOUGHER GEARCASEThe durable Torque Master Gearcase (225/250 Pro XS) features a heavy-duty propshaft and Mercury-patented dual water pickups on the front end of the torpedo for a constant flow of cooling water. The asymmetrical skeg delivers superior handling by countering the torque created by prop rotation.PRECISE HIGH-SPEED HANDLINGControlled handling at all speeds is essential, so we outfitted the 250 Pro XS with Solid Billet Aluminum Mounts to keep the engine from turning or twisting under high torque (20-inch models only).EXCELLENT EFFICIENCYExclusive Dome-Shaped Pistons efficiently direct the fuel/air charge to the spark plug, producing excellent running quality, fuel economy and low emissions.I was told factory tune is different also allowing 4% to 6% more HP. Maybe they make 2 identical motors with only a decal change but I doubt it. Dealing with a repower on a 150HP there was a price difference, maybe the decals are more expensive. Dan
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