I'm looking for the nearest comparable phrase to this in Russian. This is a relatively common expression meaning to be working at peak performance. I think more often than not it has the connotation of peak mental performance or at least does when used in a negative manner.
The nearest one I can find is perhaps
уходить с головой
like
с головой уходить в работу
but this doesn't necessarily have the connotation of performing well but being engaged.