Satoh Elk S550G with Johnson Loader, John Deere GX345 w/ 54" mower deck
I've got a 54" on a GX345 and in tall grass as long as you keep the grass chute open it throws pretty good. I keep that chute open with a bungee cord because I mow around lots of rocks and trees and just makes it easier...
I've got the 54 deck on my La175 Deere I can't imagine going back to a smaller deck, my neighbor has a 48 and he is very fond of the 54.
However his 48 deck is powered by 18hp compared with my 24hp, it takes a lot to bog it down .