If you do the maths the 6" difference means that the 54" deck would have to 10 pass to every 9 of the 60" which is SFA unless you are strait cutting 10+ acres .
Down side is they are hanging off the same width mower so the bigger deck will tilt more & scalp more when mowing rough ground or turning tight bends .
Silly city man buys 10 acres & goes to the mower shop.
Walks out with a 60" ride on, 21" self propelled & heavy brushcutter
He then spends 3 hours on the ride on 4 hours on the self propelled and another 2 hours on the brushcutter which is slowing crippling him .
He come to me & I loan him a 36" cox while I fix his 60" mower
I return the 60' mower but he wants to keep the 36" Fast Cut because with it he spends 4 hours on the ride on , 0.5 hours with the self propelled & 1 hour with the brushcutter .
It happens regularly, particulary right now as we have had 4 weeks of almost continual rain but 30 deg days so the grass is 2' long just about everywhere
The big decks will clog the chutes and require the owners to crawl at less than a walking pace while the Fast Cut will cut quite well at about 1/2 the normal mowing speed .