380 Tournament 420 cats - original prop specs?

Hi all
firstly apologies, i did try search for this but found the search function a little hard to follow under Luhrs :-(
I have a 1997 380 tournament (Convertible) running 3126 420hp cats (mechanical) a 2:1 reduction and 24x24 props.
Hull and running gear clean and boat full of our gear i can pull 2900+ rpm off tachs which have been calibrated - at cruise (2200/2300) i am getting 15/16 knots. I think i am under propped
Does anyone know what these should be (ex factory or else?)

I did find a post where another 380 tournament owner (hannah rose) with same engines was getting 2650 rpm (too low) but running 26x27 props and in that thread another poster (JW Holt) with same boat with 420 Yanmars was running 28x28s

any insight would be greatly appreciated!
cheers

alternatively - anyone with the same boat can you advise what props you are running - thanks guys
Bill

maybe on a different slant - can anyone share what spec props they have on the same boat and what sort of performance they get? - cheers