When I combined my 212 with my Marshall 410 on top, I didn't notice anything out of the norm, with the exception of having to poop standing in front of my wall of sound
Is driver mis-match REALLY a very serious concern?
No, its not a
serious concern
per se...
Plenty of electric bassists use mis-matched rigs and enjoy the resulting sound in spite of the minor degree of sonic smearing caused by a varying (depending upon the drivers & cabs which are being combined) combination of time alignment (smaller, lighter woofers reacting more quickly than larger, heavier ones) and dissimilar speakers whose combined frequency response characteristics reinforce some frequencies while canceling others (I believe this is called comb-filtering).
But, when
matching speaker cabs (with matching drivers of course) are used, the drivers react at once in unison (no more time alignment problems--as long as the cabs are evenly positioned side-by-side or stacked) + they all have the same frequency response characteristics = a more 'focused' bass sound.
I discovered this for myself years ago after I abandoned, what was in hindsight, a bone-headed bi-amped rig attempt (Yamaha PB-1-->Yamaha P2200-->2 X Bose 802 for highs + an 18" in a big TL box) for an old SVT + an 8X10" cab.
In comparison to the hi-fi rig, the SVT/8X10" proved to be about as refined and subtle as a battering ram (even more so after I added a 2nd 8X10), but it was
focused!
I've been a fan of same-sized speaker combinations (in bass amps anyway) ever since.
IMO/IME, if one cab type nails the tone one wants, then two cabs of the same type (backed with more wattage) will scale it up while preserving its character/focus.
DISCLAIMER: I am not an acoustician.