The bottom line I came away with is that I should have
sprung for one of the even more expensive ones that had
the sonic cleaning feature -- which users report leaves the
teeth feeling like they do right after a professional cleaning.

What comprises "sonic" cleaning is a matter of opinion. However, the current
Oral-Bs, and all the Sonicares, do/did a sufficiently good job of cleaning
that your teeth are "squeaky" clean -- runbbing a clean, dry fingertip over
them produces sound.