Hey Old School,
Rule of thumb is of course to reduce one inch of pitch when adding a blade to maintain RPM. It usually holds true to within 100 ish RPM. So if the 29P
4B are running the appropriate RPM the the 28P 5B will run very close. But the additional blade will induce some lift. So this can also effect the RPM. This set of props has been tested only and the props were new from Mercury Racing, as I purchased them for this client. They have less than 2 hurs of run time on them....all witnessd by myself.
Thanks!
Julie
Julie