[Fasterthanyou]

The coil almost never increases anything. The only time a higher voltage coil will help is if you are running large gaps on your spark plugs. Other than that there isn't any improved spark energy going into the plugs because the ignition module is the limiting factor. The ignition module controls the switching of the coil on but inside it has resistance to limit the current going to the coil. Most are like 8amps so no amount of coil will increase spark energy, only jump larger gaps (what higher voltage coils do).
Also the "modern" e-field coils like the ones that were used on the GM HEI setups don't go bad. They are nothing more than metal wrapped into a form. A coil can only go bad when the windings get damaged but that takes dedicated effort. Fire won't even destroy one, you'd have to short it out until it's welded itself into a solid copper ball for it to be damaged. Trust me, these things are robust and if your coil goes "bad" you'll usually find that it was actually the ignition module shorting out or loose wire connections. For this reason I always make it a point to clean every mechanical wire connector during a tune up!
The real ignition upgrades come from upgrading the ignition module to something that can handle more amps. Even that is usually pointless when the REAL bottle neck in a single coil setup is just that, it's a single coil setup. DIS wasted spark and CNP/COP ignition setups are REAL upgrades with REAL results. Also the CDI ignitions do help increase gas milage and low speed throttle responce by using multiple sparks but really they only do the multi spark to make up for the fact that they can't spark long durations like stock HEI inductive setups . Trust me, a coil isn't worth it, upgrade to CNP and you'll have an ignition system that'll never need upgrading and you can run gaps of nearly .065 compared to .045.