Biggest isn't most efficient, most efficient is turbine with lowest back pressure possible, with compressor that makes the highest needed boost pressure at lowest rpm over widest margin possible, only then can you maximize mgu-h harvesting. If you get this right you can have an extra 160hp for the whole race distance.
If max mgu-h speed is 125,000 rpm, and your turbo is making max boost between 45,000 and 60,000 rpm, and you overdrive the mgu-h to it's max speed, you have the potential to generate much more electricity than if your turbo makes max boost at 110-135k rpm. It's not hard to see how.
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