You could go with a an x749 with 3ph. Pretty fast mower. Or just about anything bigger. Bang for your $ would be LS, Mahindra, Kioti, bobcat. Just about all of the SCUTS and small CUTS would work for you. If you are looking to save time, keep the x500 for the "lawn" portions and get 35+ HP with a 6' bush hog for the fields. With a bushhog you could get by with cutting once or twice a season.
I only have 2.5 acres, but only cut one of the acres about every 2 to 4 mowings. This saves time without it getting too out of control. If I cut the 2 acres or so of grass, it takes me about 1.5 hours on my JD425 AWS. AWS saves me bunches of time and no weed eating.
A real good choice would be the Mahindra Max28XL
Believe that the long driveway is your main concern. If so, try to get some info on a York rake for smoothing out potholes. If you can spring the cash look for a quick attach feature on your front end loader to allow you to put a york rake, bucket or plow on easily. I hadf a 6 foot reat grader blade that I used for years plowing snow. problem was that if you make multiple passes the piled up snow will bog down the tractor when making the second/third pass. Hence. a front blade would make for a better clearing. Essential that you can easily change angle too. 4wd would probably be essential and make sure the tires are filled for weight/traction. As to HP. I have always used Tim the tool man's advice. Bigger is better. good luck