Ciaran. looking at the data you posted on your other post about overheating I can see that the engine has done 514 mins between 5 & 6000 RPM and 0 Mins above 6000rpm
According to the specs for your engine you are supposed to be running between 5600 - 6200 RPM - http://www.suzukimarine.com/sr_08/df...5-90/features/
The fact that the engine has spent comparitively low hours in the 5000-6000 bracket does suggest that the engine is only just able to reach 5000+ RPMs and that a lower pitch would be required. However until you get your boat and take it out for a blast you can't do much more.
If you find that MAX RPMs are below 5600 clearly you need to drop at least 2inches in pitch. However if you are up in the 5800 area you will probably be close to maximum performance.