Wow, thats a really impressive power increase. I can only wish for gains like that.

Is a 9:1 compression ratio ideal for this setup? I'm currently at 10.5:1 and haven't thought much about changing that.

10.5:1 is a lot of comp. I run it sometimes myself, but watch your fuel quality and listen closely to the engine for signs of bad gas.

Keep your total engine timing in check also. If it is high and that fuel gets flat, you are going to detonate and bend some valves.

They are really loud and run like a bat out of hell though.

IMO, 9.0 CR is good for a marine engine. You can make decent power and still run 89 octane fuel. At 10.5 CR you are going to have to be very careful and run only 93 octane fuel. You could also run some thicker head gaskets to lower the CR a little bit.