Buz, if you are looking at machines in this size, check out the Deere 5410 and 5510 tractors (65 and 75 HP respectively). I have a 5410 and couldn't be happier with it. When I went looking for a tractor I started out looking orange but once I realized I needed something bigger than the 4310, I liked the green machines better. DOn't get me wrong, I know Kubota makes great products, and if I wanted another smaller tractor I would probably buy a Kubota over the JD 4000 series, but in the bigger tractors, I really do think JD makes a better machine.
One thing to think about however, just because you have 500 acres, if all you are going to be doing with the tractor is manage the 30 or so acres of field, you probably could go a little smaller. It doesn't take a lot of HP to let the other 470 acres grow trees <ggg>.
Any chance you would share how much 500 acres of land costs in Ohio? I have 175acres and am trying hard to purchase another 100 acre and another 220 acre abutting parcels here in Massachusetts. I scan the internet all the time for larger parcels of land that are for sale all over the country, but my wife so far won't even consider moving to Montanta where you can find 1000-15,000 acre parcels for sale!....(if I could own a 5000-15000 acre chunk of land somewhere, I'd be about the happiest person in the world....)
Good luck with you 500 acres....I am jealous...