Allow me to attempt to provide an answer to your question. I think the second part of your question is easier to answer than the first part, speed, unless there is someone with the exact same boat and setup. The speed probably varies based on the propeller size/type, hull shape, weight etc. Using the stats provided by Mercury Marine https://www.mercurymarine.com/en/us/engines/inboard-and-sterndrive/mercruiser/82l/, this engine produces 430 HP, 4600 - 5000 Maximum RPM @WOT. Not sure if the engine is a Mercury Marine or Volvo Penta but it is a Chevy 502 so the brands are probably similar in HP and RPM. I would say that what you reported seems to be accurate with these stats.