WoodChuckDad, curious what price spread you've been getting from the dealers between the NX4510HST and the NX6010HST. I'm assuming you're looking at open station rather than cab, since your primary work will eventually be in your orchard, but the cabs are sure nice! Both models have the same frame size and width, with a bit more ground clearance in the NX6010 and a slightly heavier 3 pt setup to handle Cat 2 as well as Cat 1. I also assume you're test driving both models. Be sure to compare them climbing some mild grades in both Low and Mid range.
I've been a happy owner of an NX4510HST cab for 1-1/2 yrs. From what you describe, I think it would be fine for your place, unless the mowing you have in mind will be in deep grass with a rotary cutter larger than 72". I myself don't need more PTO hp for what I do, which is mostly loader work and maintaining about a mile of crusher-run private road, grading and pushing snow. The only time so far I've wanted the extra 15 hp is when I'm in a hurry pulling a 7 ft Woods box blade full of wet crusher run up a 12 to 15 percent grade. No problem doing it in Low range, I can even do it with my neighbor's generic 8 ft box blade, which I used for a few weeks before getting my 7' Woods. But no way can I do that in Mid range. And when the blade is really digging in, I can sometimes bog down even on the flat in Mid range.
Now, from my own experience and what I've seen reported by other NX owners, all the NX HST models have the same FEL capacity and enormous pulling power in Low, but pulling power drops off fairly quickly in Mid range. High range is really reserved only for transport, with no difference in road speed between the models if you are traveling on the flat. I don't know for sure another 15 hp would be an improvement for me, other than I could probably grade and push snow a bit faster by using Mid range more. If time were money to me right now, that would matter, but at this point the 45 hp is all I need. One of the tasks you list is digging thousands of holes for planting trees. For that I'm assuming you'll want a 3pt post hole digger with a 24" auger for shallow holes. I think the 34 hp PTO of the NX4510 would be fine for that. If you're going to be working in hardpan, though, you'll probably need hydraulic down force. In that case, none of the popular CUTs will have that at the rear, so you'll need to go with an FEL-mounted digger. Since you're going to be in the serious apple business, a small skidster with a front digger would be worth considering, in addition to your tractor.
Sounds like you're going to have a lot of fun, and a lifetime of projects, at your place. I'm looking forward to hearing status reports from time to time. :thumbsup: