Did at one time, if you expect to get up on plane, the 6 won't do it. If your just getting to a fishing hole then fine.
If alone the 6 would be ok, but with two and gear the 9.9'is better. When I moved up to a 9.9, mine was a two stroke Evinrude and it was fast !! With just me and minimum gear it flew, hull barely touching the water, when headed into a light wind, the front almost became airborne. Fun yes, but also scary at some times !! Question is...is your boat built to handle a 9.9 ?? Overpowering can become a liability in case of an accident...food for thought.........