I would strongly suggest you go look at a few tractor dealers and see what they have, if for no other reason than to educate yourself. Also talk to some of the dealers and ask about the sizes they would recommend. They are in your area and may have a better handle on what is being used on similar terrain.
Look at the different brands and how heavily (or lightly) they are built. Also look at different models within different brand families. For example, Befco mowers are some of the finest I know of, but there are large differences between their C-30 and their C-50 units. I would never want a C-30 but the C-50 is an exceptional unit that has every feature I would find desireable, it also comes at a high price, but again, you will pay more for high quality. I am not pushing that brand, I am simply using it as an illustration of how one premium brand, known as an industry standard bearer, can have a lower grade unit that I would not buy, plus the premium unit that others try to copy. The C-50 has spiral gearing, a very heavy weight deck, reinforced A frame and floating top link, anti scalp rollers, etc. By comparison, the C-30 is much lighter guage steel, standard gears, etc.
But I think you will do yourself a big favor if you really go out an LOOK at these things first hand.
If you were buying a tiller, that would be used a couple hours a year, I'd probably argue to go cheap. But a mower deck really is an investment and a good heavy unit will last as long as your tractor, and you will likely run more EACH WEEK than a typical person operates a tiller IN A FULL YEAR.
My old unit is for sale now, it is OVER 10 years old. The dealer has it on the lot for $950, he will take $850. That is a testiment to the quality of the deck, and there was NOTHING wrong with the deck, I traded it in so I could gain room inside my garage because I am tight on space so I changed over to a MMM.
