I think that's more a question of the size of the gap than the length of the memory. The differences between speakers, and human voices can be/often is dramatic. Identifying them doesn't require A/B switching at all; the speed of such switching is irrelevant. The differences between amps, preamps, DACs, etc. should be, and usually is very subtle if audible at all. That's where we may need to switch very quickly, or give ourselves more time to hear what we want to hear.
Tim
Tim