Has MQL proven to extend tool life as well as the top rated water soluble flood coolants, in turning operations with carbide inserts on steel?

Yes, MQL can work well in turning applications.  However there are some special considerations that need to be addressed.  Since the cuttingedge of the tool is continuously in the cut, nozzle position is critical and more difficult.  Carbide tools can work well, but it is largely determined by the relative size of the parts and the length of time in the cut.  In many cases a multi-layer coating, such as TiAlN works even better