The following is in reference to discussions we had earlier on D4 prop sizes. It is from Thomas Kempe, a volvo teck that posts advice regularly on Boatdiesel.com
"Oddbjorn: If you bought this new, contact the dealer and Volvo and ask for sea-trial data. You should reach 3600 and if not they have to fix it for you. I assume you have a duo-prop and I do not think you repitch those and instead change props. You know some engines have had valve problems in Norway and if you do not clear this with Volvo in writing they will say you are over-propped if something happens. This may happen to boats and the buyer is not aware - do not let this slip away. Nimbus has a good reputation and they can work this out with Volvo also. Otherwise change it yourself and you get some for your old props. Better to be under-propped with this engine. Gott Nytt Ar."
It seems that some are more worried about losing a mile an hour at top end rather than propping the vessel so that the engine doesn't have to lug and allowing it to reach proper RPMs. I went from a G6 prop to a G3 prop to get my boat to where it needs to be when loaded.