My immediate reaction is that a 16*11 is right. However you should not have to use 3000rpm to get 6 knots. What speed do you get at 3600? The prop should enable the engine to reach a minimum of 3400rpm (but 3600 is OK) which should give a speed of around 7.5knots.
Before you make any changes do some accurate speed measurements with a clean hull, in flat water with no tide or current, at 200rpm intervals from 2000rpm up to as far as it will go. The optimum prop should allow a cruising speed of 5,5knots or so at 2400rpm. I had a similar but a bit heavier 37 with a 2030 and that is what I achieved although with a 2 blade Flexofold - a 3 blade is really not needed for this boat engine combination.
a decent Volvo agent should be familiar with this process as it is basically what is required when commissioning a new installation. When they talk about wearing the engine if the prop is too "big" they are referring to what is known as overpropping which can indeed if extreme overload an engine. However what you describe is the opposite - the prop seems too small. As a guide 1" of pitch change will change revs by between 250-300 so if the speed/revs data is correct going up to a 16*12 will drop the revs to a more reasonable 2700 - still a bit high but acceptable. As another rules of thumb for this size prop a change from a 2 blade to a 3 blade usually means a reduction of either diameter or pitch of between 1and 1.5".
Slight word of caution is that the Volvo 3 blade is an unusual design and calculations for more conventional props which I have used may not necessarily translate directly. However, if your data is right (and your hull is clean) it is not satisfactory.
Hope this helps
