The L3901 loader lifts about half as much. So it comes down to how important unloading those pellets really is. I'd guess you're doing it a few times a year. If you have a second pallet, you lift it up with the tractor beside the full one, drag a few bags off onto the second pallet, lower it a bit, do a few more. Take that inside, come back and lift the remainder on the original pallet. It's not ideal, but if it's only a couple times a year then it'll be fine.
So then the only material difference I think you'll see is "working the fields". How real is that really for you, and how serious about it will you be? You only have about 7 acres, can't imagine you'll plow and disc every year. Which means it'll make no sense to actually buy those implements - you'll borrow or hire it out. If you borrow implements, you could just borrow the tractor that pulls them as well. If you hire it out it'll come with a tractor.
As with all these things, you're at the point where you need to decide if you're buying for things you might do, or for things you'll definitely do.
Of course, easy to say that to other people. Later this year I'm changing my BX into a B2601, and I have about 1 acre of flat ground that I mow. There's almost nothing that I do that the BX can't do, but I want a B2601 so I'm getting one. Arguably it'll pull the boat better, and a couple times a year I run out of lift on the 3ph with the BX.
Just be clear what your reason is. If you need the MX for some jobs you're actually going to do, then you need to buy it. If the L3901 won't do the job then no point in buying it. If you want the MX because it's a bigger more capable tractor and it makes you feel good - it's your money, and it's only $7K. You'll have it for 20 years, and I doubt you'll ever regret it. People spend $80 a month on things that are much less useful - hell, having that smaller truck is probably saving you more than $80 a month. If the tractor gives you more joy than the truck did, then that's money well spent.
