I would imagine in some selective feeding situations, going below #22 is required. Hanging a something really small off of a Griffiths Gnat probably works well during a hatch. Then again, I'm not a big midge guy, I usually employ them in nymph form only, usually mid-summer, fall, and winter. Most of the waters I fish also have really healthy caddis populations, so I'm sure they get mistaken for micro-caddis since midge and caddis profiles are very close in the larger sizes (16-20).
I like the 2488 when you start getting small because of the straight eye, gives you a tiny bit more hook-gap, not sure if its makes a difference, but its a confidence thing.