The answer to all this is in the torque curves. As you say Danny 2800 is the max on the Amel TMD22A installation. This effectively limits its max OP to approx 60HP. I have been very happy with this performance for the past 14 years as are many other owners. Looking at the torque curve for the TMD you will see max torque is at around 2500 RPM, hence its susceptibility to a fowled prop/bottom. Compare that to the hugely bigger torque at similar RPM on the D2-75 and that is why it will push through to its advertised rpm despite the fowling.
Amel should really have rebadged the TMD22A with a 60HP label.... but of course thats not what sells boats! Given that I've been very happy with a "60HP" engine for all these years its the main reason I'm looking at the BETA 60. It has no turbo and no electronic control boxes and will fit very comfortably in the space. At cruising RPM (2000 to 2100) that will give 7kts it produces 170nm torque compared to the TMD22A...same RPM but153nm torque. The beta tops out at 2700 rpm. So essentially it does exactly what the tmd22a has been doing all these years...but without the turbo.
The BETA man is coming to the boat on Monday I'll keep you posted on how it all goes.