Nice work John!

Once you've got the basics right, finetuning a boat is often a matter of trial and error, as you've found out...

Going from 48 to a 55 is a huge step, be careful and watch the temperatures.

Usually the bigger props have a higher pitch, I've used that trick to make use of the extra runtime I had on my 12 cell 700 motor Flash; I milled down and reshaped an 48K to 45mm, this allowed me to run a coarser pitch and still keep the motor revs up.
The boat speed increased about 4-5 mph without creating more torque issues.

I still have be gentle on the throttle, accelerating out of a turn, when I run this modified prop...

Regards, Jan.