Is it a Tohatsu/Nissan brand ? A 10 footer is rather small, will have huge hull drag to overcome fast, larger is always better. A 3.5 HP OB pushes a J-24 sailboat at max 4-4.5 knots at wot on flat calm no windy open water conditions.
With your actual setup probably max 5 knots. Won't see much speed difference going from 3/4 to full throtttle, 3/4 is a good setting. Inflate that sib to it's max factory recommended working pressure and ballance deck weight evenly for best overall water performance,
Happy Boating