You are correct, Mark.It sounds like you're unfamiliar with Lusitania and Mauretania.
The 'real life' experiments of both ships with numerous different propeller configurations is well documented, including four bladed units and three bladed units, as well as a mixture of both on the same ship!
The experimentation of Harland & Wolff with different propeller configurations for Olympic, Titanic and Britannic is also well documented.
I was asked for my thoughts and based them on simple logic.
However, as a former Builder's Risk surveyor at John Brown's old Yard, Clydebank, and as a serving officer, I am familiar with experimental trials on ships and many other marine craft.
Now back to the subject.
If this change of central propeller was indeed experimental work then we are discussing an experiment on a new ship which had to have been contemplated before there had been enough time to evaluate the performance of her sister - a sister which had only been in service for 3 months before having to return to dock for repairs and had only completed 6 monthsof her live before having to go back to drydock once more. The WSL shareholders and The City must have been having deep thoughts about the future when Olympic arrived back at Belfast in early 1912. Hardly the time to experiment would you say?