Yeah, it all depends on what you want to do with your land. I have 68HP on 10 acres (well my son uses it on his 5 acres too) and I could use it on some other property, too, but the real issue is always what you are going to do with your land and of course how much you want to spend for a tractor. The cost of a tractor and implements is significant, but over 25 years, it is about equivalent to renting a tractor and implements for three or four days a year.
I use mine to cut ditches for drainage and it takes a lot of power to push a blade into the ground to cut a ditch a foot deep and two feet wide with a single cut. A box blade can completely use up all the traction of very large tires and 4WD with both front and rear differential locks locked. A box blade full of dirt weighs close to 4000# and cutting while climbing a slight grade also takes a fair amount of torque and traction. Tillers can take a little or a lot depending on the size of the tiller and the condition of the soil. A rotary cutter normally takes little HP unless the grass is thick and/or high.
A tractor becomes your mule and it's ability to pick up very heavy loads is not an insignificant task. A pallet of feed can be over a 1000# and with two of them on a pickup to unload, you have to be able to get the front one out. Picking up heavy objects is also really nice, but the exact weight you can handle or need to handle depends on the tractor, ballasting, and the loader. Mine only handles 2200 pounds at full height, but that has not let me down yet. Pulling fence posts takes a fair amount of pull, but sure beats any other way of removing them. Moving materials is a lot different in the amount you can handle each load with a 4 ft, 5 ft, or 6 ft bucket. A 6 ft bucket can weigh over 2000#. Being able to pull a stuck vehicle out of the mud is sometimes convenient. The more you use a tractor on a small farm or ranch, the more things you find you can do. The older you get, the more important it becomes to have a good mule.
Kubota makes the best hydro transmission on the market, hands down. You cannot get a hydro in tractors much larger than 40 HP. Since you will probably never pull a bailer and may not cut your own hay, the necessity of a 50HP tractor is considerably less. I have a gear drive and that serves my purposes well. I normally go forward in one gear for several hours and a hydro would be of no real help to me most of the time. For the few times doing landscaping work around the farm, they are really worth having. They don't do as well with a sprayer, or fertializer spreader or anything else that the operation may be dependent on ground speed being predictable.
Finally on 4WD. Just can't say enough about how dissappointed I would have been if I had not got it. About 90% of Kubota Compacts are sold with it and about 50% of the M Series (40 HP and up Ag tractors). I had a 2WD before, and it is absolutely worth what it costs in a Kubota tractor.
The Ag tractors are actually a little cheaper than the L Series compacts, but do not have some of the neat creature comforts and conveniences, although I am hard pressed to say there are any that I miss not having on my tractor.
