If the spark can initiate combustion, the engine will run.  Beyond that, it is a matter of efficiency.  The fact is, there is a finite amount of time for a mixture to burn before it exits the engine as exhaust.  As the RPM increase the shorter this time becomes. 

    An analogy to demonstrate this is to take a sheet of paper and light it with a match, the paper will burn in " x " amount of time.  If a larger flame were to be used to ignite the same sheet of paper, the subsequent larger flame would consume the paper in a shorter period of time.

    Both methods will burn the paper, but if there is an finite amount of time to complete a burn, the larger flame would be better. This does not imply that fuel burns slowly in an engine, it is just the opposite. Fuel actually burns very quickly, however we are talking about only milliseconds of available time to completely burn in the combustion chamber.

    The T-ReX coil kit was designed with this concept in mind.