I have an 03 Sunsation 288 with the 500hp efi hooked up to the bravo XR drive 1:50 ratio. WOT I'm running about 4800rpm with a top speed of 71mph with the bravo 1, 4 blade 26p prop. Boat runs strong, some mods to the engine, pushing around 565hp. Would I benefit switching to a 28p prop or perhaps a 5 blade to get a few more mph?

My guess is send your prop out have it pitched down to a 25 and have it labbed. I have no idea what you did to your engine to make more power, but in order to make that power you are most likely going to need to spin it harder that before. A stock 500 EFI should be propped around 5200. So as it stands you are 400 rpms off. A 24 would put you at 5200, having it labbed would put you at 54-5500. Either way, a 28 will not work at all, it will reduce your rpms down to 4400, and there is no way you will gain speed by doing that.

Have you tried a 25 Mirage plus three blade prop. If you can get on plane it will be your best prop. Less blades for top speed, More blades for fuel efficiency and best cruise speed at a given RPM. You won't be able to spin a 5 blade prop.

I never thought of having it labbed to a 25p. Didn't do much to the engine, swapped out the stock heads and put edlebrock heads on and running a different cam. Thanks for the input, I will look into getting it labbed!

Never tried a 3 blade prop. Not a lot of people in my area to get props from and try them.

I doubt any 3 blade will work well.

You are not even turning enough rpms at WOT now. You want to spin that engine around 5200rpms at WOT. A 28 would reduce rpms by about 400.
Get your current 26 labbed by BBlades.

Seems to be the direction I'm headed. Already checked them out online and will be calling Monday!

Out of curiosity, what cam did you put in your engine. The stock cam is a pretty respectable cam.

I have a nice Mirage+ 25 pitch (L/H) for sale. Also have a nice 27 Mirage + R/H for sale if that would help you.

Why do you think a three blade prop wouldn't work? If he hasn't even tried one. IF you can get on plane three blades would be faster than 4 blades and it would raise the RPM also.