Yankho
I just bought a JD670 and love it after 15hrs and three projects - moving rocks,fencing,and clearing dirt. My brother gave me some GREAT advise - try getting on and off from both sides moving the machine between each mount. You'll quickly figure out if the controls are poorly located or yor to big for the machine. Also think about your property and current buildings and access. I,m widening access next to the shed to six feet with a bigger tractor I would have to go to 8' or more. I have narrow trail on my forested property and the 670 will navigate just fine.
The trade off on size will be time (besides $) you may have to make 50% or more passes or trips to till, level land, move material ..... Visit with some locals and find out what they use their equipment for.
Best wishes Ron JD670