The L3901 is a lot more tractor than the LX3310. With a tractor weight is often what does the work - and an L series is a good 500lbs heavier. Many of the components are also stouter, including the rear axle and gearbox.Oh it's not that bad. Why the L3901 over a LX? I just looked and the L3901 is about the same price as a LX3310.
The LX has more luxury features. The L has more metal. I guess it's a question of where you spend the money, and what your use is. For me, my property is small and I wouldn't have any use for the extra power. My B2601 is plenty of tractor for what I do, and I like the more upmarket features.
You've got a lot more property than me. I think you'll work your tractor harder than I do, you've got a long driveway to do snow work on, and a big field to mow, even your lawn is big. The L is a more robust piece of equipment, it'll work harder. The L3901 gets you more HP than the LX3310, and it's non-turbo. Did you say you're at altitude? That'll impact the L more than the turbo LX. I'd expect it to have more grunt low down, and to be a bit better at things like box blading and brush hogging - being a bit bigger and stronger.
It's all horses for courses. They're both very good tractors. At the same price I'd be pretty tempted to get the bigger one, it's well known that bigger is always better.
If I was getting an RFM, I'd go bigger rather than smaller. If you're using a brush hog, then you can get used to an RFM. Again, I personally like my MMM, but plenty of people have an RFM and swear by them. I think you can get them with rear discharge, which leaves the clippings nicer, and you can push them under trees in a way you can't with a MMM. Flipside, a MMM you can look down and see where it is, a RFM you have to turn behind you, and they're a bit less intuitive around obstacles - sometimes hard to get close until you've had practice.Not sure if i could get use to a RFM. Maybe i should buy one and see should i get a 5 or 6 foot? Local dealer has both on the lot...landprides.
6 foot easily with a 33 or 39 HP machine. 5HP per foot is the rule, and I think you can go a bit more than that with an RFM (whereas with the brush hog I'd probably stick to 5HP per foot). It's supposed to be PTO HP though.....but it's only a rule of thumb. 6 or 7 foot with the RFM. 6 foot is 72 inch, the LX2610 comes with a 72 inch MMM. I personally think you can go a bit bigger in an RFM, and given you have more HP than the LX2610. But of course the question is what you're mowing. Sounds like you have 2 1/2 acres you'd be mowing often. That's probably a good hour and a half or more of mowing, a 7 foot might make that one and a quarter instead.
If you look, you'll also see a lot of people commenting on the rough ride of their tractor when mowing. I'm a fan of a wider mower running slower, rather than a narrow mower running fast. It's easier on your body, and gets the same amount of lawn cut.