I am going to have to disagree with Jules on this one.

NZHobie, I think you are on the correct track. You want to start with your forestay in the top hole of your adjuster plate. Tighten your side stays as evenly as possible. Then throw your main sail up and see if you can still sheet in block to block or not. If you can sheet in block to block but your sail is not very tight, loosen up your side stays and tighten your fore stay one or two holes. Then test it again.

The idea is to get your mast back far enough where you can almost sheet in block to block, but still have a good amount of rake and have the main sail tight. Then depending on the conditions, you can do fine adjustment of your mast rake with your jib halyard.

The aft angle of your mast is an important performace tweak on cats. Once you have your mast set where you want it, you might want to think about adjusting the rudder rake also.