breaker panels: 200A 30/40 vs 40/40
I'm looking at two panels from the same company (one of the big ones) and they make two nearly identical panels (200A, convertible main, same neutral and ground layout, bus, etc.).
One is 30 slots with 40 circuits and the other is 40/40. The former is a little cheaper and comes in some useful package kits, and I don't have to mail order it, but the latter has the full 40 spaces.
The question is really this: is there a situation where it would be advantageous to have the 30/40 vs the 40/40 (aside from a tight space). Are there any breaker styles that only fit in the double-gang slots (they would be QO-type, BTW).