I believe ( and I may be shot down, but I am always willing to learn) that the fact that a sports coil MAY be capable of delivering saaaaaaaaay, 15000 volts instead of 10000 volts is largely irrelevent.
I believe that voltage will rise in a coil much like pressure will rise in a pipe. Once the limit of the pipe is reached (lets say 10000 psi for instance) then the pipe will burst and the pressure will not rise anymore as the container has collapsed.
Same with a spark plug, once sufficient voltage is reached for the spark to "break over", current will pass through the coil, Ohm's law will come into effect and the voltage will collapse as the coil discharges.
The best use of higher rated devices is that they may last longer because of superior construction and insulate, or that you may run plug gaps that are a little wider than usual as the voltage is capable of reaching higher values to break over slightly larger gaps.
Turbo cars have a use for them as well as boost pressure rises, the spark will not as readily jump the gap. Essentially blowing out the spark.
But for a normal everyday use, the possibility of a longer service life may be the only gain, everything else is a waste of money IMHO.
Please correct me though as my humble knowlege of auto electrics may be flawed
If you want this coil type for use with a Pulsar dizzy, get the GT40RT, which is 
two week looking for the problem and $60 of a specialist to find the problem 
