IMHO running a hotter coil can improve combustion, but you need new spark plug wires as well. To gain the full benefit of the higher output coil, depending on the new output voltage you would open up your spark plug gap roughly another .010 to get the most out of it.
I have ******* around with a bunch of that performance stuff and honestly on a fuel injected engine running properly I never saw any gains. Although if you read up on the "six liter tune up" you will find lots of guys claiming great gains. Often I have wondered if they had other problems, like their local fuel supply was ******* or low compression, maybe weak, leaking injectors, worn rings that type of thing because I have tried it on a couple of vehicles and did not see it, however I did create problems. Twice I have had the aftermarket higher voltage coil fail on me in the middle of nowhere. I put the OEM ford back on, even with the larger spark plug gaps and had no more problems.
If it is an older Carb engine, especially with a points distributor there is great advantages moving to a pointless, HEI system. May not feel the HP gains, but it will start easier, run smoother and improve MPG.