Have heard from a few owners that when they switched to lithium batteries that their boats actually lost speed. Being someone who has owned ultra performance bass boats in the past (Allison, Stroker) which were very light and fast because of this to lose speed when going lighter does not seem logical more so w\since we are not talking about a lot of weight (100 pounds +/- depending on how many batteries versus lead cells).
Less weight means less load, more RPM’s, and hypothetically more pitch could be added which equals more speed.