Rounding a turnpoint in sink

Mark Navarre wrote:
Any manuvering as in b or c will cost more than a plain efficient
turn,

That is not necessarily so, since a 180 turn at a high speed, even
if cleanly performed, will use up much more energy, and take longer,
than one at a lower speed.

It is not really possible to tell which is better simply based
on whether you are maneuvering or not. You'd need to do the math.
CV