currently running Bravo1's 27 pitch at wot running 4500 rpm's twin 502 mpi Mags.

Labbed B1s? Considering they are offered even pitch's. If your WOT range is up to 5k, they I would it depends, first on what yourt 27s are, then go from there. THen is that light or heavy and what load do you normally run.

Then we can determine what you need. Assuming you have a straight bottom fountain? Based solely on 4-500 rpms needed, 24-25p would gain those rpms.

25 hydromotives , spinning "inwards" ...

my fountain is a single step hull and normally runs in the low 70's

4500 is putting you probably just about at peak tourque / load on that engine ... hard on that engine

Should I step up in prop 27 to 28

No! You need to step down . You are overpropped now. Which way are your props rotating

I think out but will check this weekend

Fountains need to spin in! They left the factory that way for a reason, they run best that way. On my single step 35 I ran box stock Hydro 4 blades and Merc labbed Bravos. Both ran same top end speeds, Hydro were better handling in slop at high speeds, Bravos were better every day cruisers. Far as pitch with HP 500's, Hydos were 26's,the Bravos were Merc labbed 28's. You will need to size down to your power, look to the factory for the perf report and start with what the boat was shipped with. You need to get the revs up, that is too low for those motors.