I don't have anything to add for OP except regular 54 (BX23, takes BX22 deck) does just fine...
However, I've been reading on this for a couple of years and confusion reigns!
Looks like there have been, and still now are 54 finish, 54 fine, and 60 finish decks offered. (From various pictures I can tell 54 fine is a 'deeper' deck.) I'll go as far as to guess that the extra depth affects airflow, somehow creates more vacuum, stands the grass taller and thus cuts appear more uniform when the grass falls back into the relaxed position (kinda like the old days at the 'hand and scissors' barber). Now, I'll also guess these mulch kits affect airflow, as the theory seems to be that suspending the grass above the blade allows it more time to be cut over and over. So that leaves me wondering...
Do all 3 mowers offer mulch kits (for sure?)
Wouldn't a mulch kit, if offered, actually move or reduce the fine deck away from 'fine' mode (change the airflow such that the grass suspension is above rather then under the deck?) Kinda seems to me 'fine' and 'mulch' contradict each other both in theory and aesthetics.
Also - since there just might not be enough variables in this mix, how does the bagger fit all these combos - for those seasons when 'mulching' isn't appropiate (like coming home from vacation)? Would one remove all the mulch kit, or just remove a chute plug and hook up as normal?
And my own query - if I made little triangles that stored on my deck could I drive over it too?