Often, it's just the dealer's own marketing. There may be no significant difference in overall performance between the products. You should contact the dealer directly for an explanation of what makes them all different and see if they even have an answer!
I've got a Level 1, 2, 3, etc package, but that's really just a numbering differentiation more than anything. The level 1 and 2 CDIs are operationally similar, with a heat sink cooling fin assembly on the Level 2 CDI. Level 4 is an adjustable CDI, so that's clearly a different product. (Level 3 is the Level 2 CDI with a coil added to the package.)
Basically, as the guys have said earlier in the thread, the CDIs will be functionally similar with different timing curves in the higher RPMs, and no artificial RPM ceiling.