If you gather solid observations of your gear ratio, GPS speed right before you hit the rev limiter, and RPM at that speed just before you hit the rev limiter (5200?), it'll give a much better idea of what props will do well for you. Especially if you can do it with a light load and with the boat trimmed out nicely for speed. From your description with that 27" 4-blade Bravo1, not sure a 28" is enough.
(If you don't have a GPS, you can download a GPS speed app for your phone.)
Sounds like it's really running though, congrats.
"I don't have time to get into it, but he went through a lot." -Pulp Fiction