Which suggests to me a heuristic to tell which of two memeplexes is closer to the CEV of humanity: is the fraction of adult A-ists who convert to B-ism per year larger or smaller than the fraction of adult B-ists who convert to A-ism?

If you're curious, you could try doing this heuristic on the Pew American religion survey which includes rich conversion data: http://religions.pewforum.org/pdf/report-religious-landscape-study-full.pdf (The results may surprise you!)