Only way to be sure is test them all in a lab, or there should be some maker's markings on the coils and a number (e.g TEMIC, Beru et al) and you can find the KV rating online. There's only so much KV a coil winding of that size can kick out and I'd be surprised if there's any more than 5KV difference between all of them, which you won't really notice.
Even if there is was an appreciable difference in spark strength, the coil dwell (charge time before firing) may be different in each application, so you wouldn't get the full benefit anyway. Different coils need different charge times to produce their peak output.
A stronger spark might help if you're running big boost and gappier plugs, but if you're not getting misfires under hard load, I wouldn't bother personally.