How fast should I get?

[Seacrets]

I don't think the idle setting will change the top end. I would say you should be running about a 17" pitch prop for good performance. Try a gps. The boat speedometers are highly inaccurate. I had a 150 merc on my V20 and I maxed out at 42 mph with a 17" pitch four blade prop. There's a bunch of guys on here with your same setup. You should get some great feedback. Good luck.