Before discovering this community, it hadn't occurred to me that the whole "after 30 or childbirth" thing is just a rough guideline, and that maybe I should try larger cups despite my age and lack of children. Since going off hormonal contraceptives, my periods reverted to being unreasonably heavy in the first couple of days, so even though I was generally happy with the small Diva, I had to use substantial backup. After doing a bunch of reading here, I decided to give the large Lunette a try. Its design really appealed to me for a number of reasons, but after using it for a few cycles, I had to admit to myself that its stiffness is just too much of a disadvantage for me personally, and that its capacity isn't actually much greater than that of the small Diva. I then contemplated getting a large Diva while I was visiting Canada (locality does, after all, contribute to the overall "greenness" of a product), and also considered a large Fleurcup on the basis that it also has a very high capacity and is apparently slightly squishier than the large Lunette, but I ultimately bought myself a large Yuuki because of its yet unsurpassed capacity, alleged squishiness, and awesome price potential on eBay.
Wow. Best. Cup. Ever.
For me, anyway. The capacity and stem length are both working better for me, it's easier to keep clean than I thought it would be, it's wonderfully, comfortably squishy, and I'm actually finding that it pops open more easily than my small Diva does. The only real improvement I can think of would be a flat or solid stem (which apparently some of the older ones have). I'm pretty damn happy.