Treeman is correct. There are dozens of decent brands of commercial mowers, but you need to buy one with a long standing dealer near you who can get you service and parts when you need them.
If you have a real flat yard, a 60" would be OK, if it is lumpy or uneven in any way, a 60" will be too much and start scalping. Remember, the bigger the deck, the more horsepower it consumes.
I have a 52" Great Dane Chariot with a 25 hp Kohler.
The Scag Turf Tiger has some design features I really like. The crankshaft is horizontal, The belts are on the very rear, the hydraulic pumps are mounted horizontal outboard of and below the engine, thus the belts are very accessible. One of the pulleys drives a shaft with U-joints that runs forward to the deck to drive it. Eliminates the long deck drive belt that constantly runs in mis-alignment due to the deck being adjusted up or down and the deck and drive pulleys in a belt drive system not aligning. This is the cats meow, but you do pay dearly for it.
My Great Dane cost $7000 in year 2000. Some of these mowers can get up to $10,000, 12,000 depending on the engine and deck size. It is and will be the last mower you will ever need to buy, so shop carefully.
Scag
Toro
Grashopper
Dixie Chopper
Hustler
John Deere
ExMark
Country Clipper
Land Pride
Simplicity
Swisher
Ferris
Kubota
Massey Ferguson
Bob-Cat
Yard Shark
Husqvarna
Snapper
Bunton
Bad Boy
Great Dane (designed by Mr. Dane Scag, inventor of the Scag mowers)
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Charles