One you left out, that may be important in an otherwise skinny month: IA pays double without regard to any "trigger"; a GS only pays double for that portion where one's credit is above the trigger.

To the OP, that's one of the more important practical differences between credit/no credit, btw--if you're GS'ing, make sure you know how much credit you have, otherwise you may not be getting paid what you think you're getting paid....