I'd probably lift them now and let them cure in a shady area with good air circulation. Normally, once the necks in garlic get soft enough for the garlic to fall over, the leaves aren't providing much in the way of nutrients / growth to the bulb.

If you wait too long, all the wrappers (skins around the bulb that the leaves are supporting) will disintegrate and you'll have a bunch of loose cloves when you dig them up. The garlic will be usable but since you've lost the protective layers around the bulb, the garlic will dry out faster and thus not store as long. It'll still store long enough to re-plant in the fall though but I usually just use any like that for pesto.

That looks like pretty darn nice garlic even at that size - congratulations on the first try!

i have a related question. We had a terrific windstorm a few days ago, 60mph gusts, strong even for Kansas. It blew over and broke most of the onion and garlic plants that were growing. What should i do with the onions? my galic was already large enough that i can harvest it, but my onions need some growth...will they continue to grow?