I am not convinced what Murdoch would have understood as the best thing to do. Presumably knowing there was a berg rather close, that it took a considerable time to stop the ship, probably he could have seen it would be far too long, having chosen to try to turn her away, I dont see why he would have cut propulsion which would have reduced his limited ability to turn away. Yes, ordering stop on the relevant outer propellor to help with a turn, but ordering stop on the other propellor would presumably make matter worse. So I half agree, half disagree, that he might have chosen to stop one engine, not both. The central turbine ran off exhaust steam from the piston engines, so presumably would have lost half its power if one side engine was stopped (I'm guessing more than half allowing for inefficiencies), which might also have impacted on the performance of the rudder, situated behind the flow from the centre propellor.
The other problem I see, is that Murdoch if he understood his job might already have anticipated he would need to immediately turn in the opposite direction to cancel the rotation of the ship. Maybe he was hoping that the ship would swing gracefully away from the ice in one smooth curve, but presumably familiar with difficulties coming into docks with land closeby, he must have been well aware of the necessary reaction to cancel a full turn in one direction by reversing the controls.
It sounds like the sort of question which needs to be adressed to someone experienced with handling a big ship, faced with making the best of a no win situation where he decides to try to avoid collision but knows this will be very tight if it works at all. The basic physics of getting large masses of metal to stop moving and then start again in an opposite direction hasnt changed.
I understand Murdoch was probably one of the very most experienced people in the world at that time with handling such large ships. Of course, not least because this was the biggest ship in the world. I'm not sure if that is an impressive qualification, or a big risk because no one was really experiencd with such situations. I think it must have hampered official understanding of what had happened that there would be hardly anyone impartial with real experience who could have been called upon to analyse what took place. From what I have read, I think he must have understood this was a situation where he probably could not miss the berg and could not stop, and would therefore have planned what he would do on that basis to minimise damage.
I am also not clear whether he would have known that ramming the berg was probably safer than grazing it. He might have, which might then itself imply he thought he had a chance to avoid collision completely. But even if he felt grazing was better than colliding, obviously avoiding was better than grazing, he must have been thinking about the best way to do it given the limited control he had on engines or rudder.
How good was he at his job?
By the way, its great to see posts from people who have had some actual experience with such machinery.