Well here is the wording out of one of my training books I have from over the years as it states about how the ballast of course heats up some at low eng speed since the points are closed longer and creates more resistance in the ballast and keeps the primary ciruit level lower. Then it says......this action servers to keep the coil primary winding cooler and improves dist point breaker life. At high speeds the points are not closed as long so the coil primary has less time to build up its magnetic field so that means with less current flowing time wise because the points are not closed as long the ballast cools some and has less resistance so the coil will still build up as much in the primary winding since the voltage is higher to compensate for the less time for the coil to saturate.
Many times over the years I have read the same thing as the ballast saves point life and limits the primary circuit current flow at times. And yes I have seen some coils get very hot on some buddy's cars when they use the wrong ballast or coil and let more current flow in the primary circuit. So thats one reason I wanted to make sure my coil did not feel real hot as that would have had me checking more to make sure I did not have to much current flow in the primary circuit.
Funny as when GM when to electronic ign they stopped using a resistance wire in their ign and run a full 12 volts in there HEI. Ford like Mopar still used a resister wire which had to be for either the coil or the electronic module to limit current flow and not let them overheat. Myself I felt that I should leave the ballast in because thats how Mopar made their system. But like I said I read a few mags about where they took it out on the Mopar electronic system and it worked well which mine does. It may also make a difference that I use the 4 pin ECU and of course Mopar had the auxillary circuit with the 5 ohm ballast on the 5 pin ECU.Of course the only ones that have bypassed the ballast like me are all the 4 pin ECU. I know I am not the only one running it like that. Sure it may be able to put out more voltage output at idle since it has no ballast but it will only put out what it needs to jump the secondary resistance and the plug gap anyway. And on the electronic system we cant adjust dwell anyway since the ECU controls it and some ECU's can change the dwell some to limit dwell time for lower speeds and output or increase it but of course it can only give so much max dwell. And electronic ign can keep a constant voltage if the system needs to by controlling dwell as none of the electronic ign systems have used a ballast the last 20 to 30 years. Also GM and Ford used a resistance wire in the wire harness on their point systems that did not change resistance by temp and current flow like Mopars ballast did so they must not have had a constant primary current as well as the cars with the ballast type ign resister.
So my point is the heat and temp of the coil does matter. And the ign system will work fine without the heat/temp style ballast since the coil will only put out what it needs to overcome the full secondary circuit. Ron