I am in the process of rebuilding the engine in my 25ZX Donzi. I was spinning a 23P Mirage Plus with the tired stock 502 MAG MPI right under the rev limiter. I also had a BBlades lab finished 25P Mirage Plus that ran a few times but was just a tad bit to much with the stock engine. Of all the props I tried, the boat responded best to this prop (Also the prop that came on the boat from Donzi). The new engine will be real close to 550hp and I need some advice on where to start with the prop testing. I am not changing the X-dimension yet, so I assume I would want to stick with a Mirage Plus as that hull seems to like it? Wondering if I should start with a 25P or a 27P? I also have a labbed 28P Bravo to try, but I think that might be to big. Any advice would be great.

Start with the 25 Mirage+ that you have. Did you raise the rev limiter with the increased HP????
I think the issue going to a 27 Mirage+ is that it will probably be very hard to get on plane and will most likely break loose easily.

I have a 27 mirge plus labbed to a 26 by BBlades , i bought it a couple of months ago and i thing it going to be to small and i have a shorty on my boat
pics on demand $ 300.00 shipped

Run whatever you can get your hands on or already have. Compile that data in writing. We can use that information to determine the best move.
We can then use our test program to verify the best casting to work with.

Brett