I've got 17 years use through 2 Sears riding mower 42" decks. Sears is great because you can always get parts for them.
I'm now in the market like you, I have a couple acres to mow.
Sears has a new "pro" line in yellow paint you may want to look at.
Sears: Online department store featuring appliances, tools, fitness equipment and more
That said, Home Depot has a good selection, and I'm looking at the Ariens/Husquvarna line like the 46" with 22 hp V-twin for $1500. Yes they have a 54" too.
Outdoors - Outdoor Power Equipment - Riding Mowers - Gas Riding Mowers at The Home Depot