I read your post in the yanmar forum and honestly think all these tractors are too small for your needs but I will say that I am fond of Mitsubishis and have owned several of them, varying from 1600-2800 series. I currently own an MTE 2000D that I've had for about 8 yrs and it's been excellent in every aspect.
Anyway, to comment on these specific tractors, I think 4 wheel drive is a must for compact tractors so the D1650 is out. I then go to bigger is better so the 1850 gets the nod over the 1601 since both are 4wd. Very few Mitsubishi's have 2 cylinder engines while Yanmar has several popular models that are....I'm not particularly a fan of any 2 cylinder engine ( they're torquey but clanky and knock), Mitsubishis 3 cylinder engines are smooth and reliable but their 4 cylinder models ( which are numerous) are even better and that gives the 1850 extra points in my book. Now comes the most important consideration...parts availability. This I can't answer for you. The 1601 seems to be the more popular model and I feel more comfortable saying that parts are as common for it as about any Mitsubishi model. I don't think the 1850 is a total oddball but I just don't see as many of them. I know it is a slightly older model than the 1800 and 1801 models but not sure if the differences are enough to make parts a big issue? Maybe one of the dealers will jump in and give an opinion. I would also like to address Parts. Undoubtedly, Yanmar has the best parts support of the grey market brands but they have models to avoid just like everyone. I think Mitsubishi is a close second in parts availbility. When dealing with these older tractors, there are always going to be some parts that are hard to find/expensive/etc...you can find that with some older U.S model John Deere, Ford, Massey Ferguson,kubota, etc too though. Just be sure you buy a popular model that has good parts support, regardless of who makes it. You didn't mention price on these tractors so I can't tell you if any of them would be a good deal. I know you are already aware of the Vietnam recon issue so that doesn't need to be mentioned.
All this said, with 11 acres I'd hold out for something larger and preferably with an end loader. I know that's a tall order when on a budget but patience is the key. I know that you are also looking within a limited area. Try expanding your search and consider using a shipping company if you need to. uship.com is a great way to get competitive shipping and to give you an idea, I would say a 30 HP tractor shipped 1000 miles would average about $900. Just trying to give you some ideas to help give you more options.
