I dare say the EC-155 purchase by Shell was not based upon any kind of efficency study....quite the contrary. The Bell 412 that showed up at Redhill with all the fancy kit, buttons, knobs, and dials was not even looked at. That was a Shell decision....not a Bristow one.
The 155 was to replace the 212....but cannot carry the people and baggage the 212 does....one cannot load passengers and baggage simultaneously as you can on the 212.....the 155 requires much more "runway" to operate than does the 212. We even did a VIP run into a ball field because the 155 could not operate into the place.
The 155 is faster, smoother, has all the fancy kit....but is not the aircraft the 412 is for offshore or utility type flying.
Ask 212man about the new runway being built at Warri to replace the 212 site that has been used for ages so the 155 can legally operate out of the Shell IA. All of that is a function of engine power or the lack of....