2002 Classic, SI transducer location

I just purchased a humminbird 798 ci SI to go on a 2002 classic. Any help in where to mount transducer. Should I expect to lose depth readings at higher speeds. I currently have a lowrance lms480 that maintains depth reading to 55-60 mph. Any help would be appreciated. KentKent Charles 2002 Pantera Classic & 200 Yamaha VMax