I don't know about the F150-F250 analogy, but yes the M is more Ag oriented with the geared setup and heavier frame etc, but you have to ask yourself if you really need an Ag oriented tractor as opposed to the utility
L5740. The
L5740 is a pretty powerful tractor capable of a lot of work. TexasJohn uses a
L5030 like mine on his 200 acre cattle ranch and others do a lot of work with the L Series. I pull a 7' box blade with my
L5030 and it does not have the power of the
L5740.
I own a M8540 (my avatar) which replaced a Case CX80 because I need a more Ag oriented tractor on one of our farms and use it to pull a Woods DS1260 rotary cutter.
From your description of your property and tasks, my choice would be the
L5740 due to the ease of operation, (my wife drives ours), power and comfort. She will never be comfortable with the gears or shuttle shift though in time she will be able to move it from one place to the next, but will never work with it.
There is absolutely nothing wrong with the M Series, but for loader work and such, I will take the Grand L any day. Now if you were doing a lot of heavy pulling and ground engagement equipment, different story.
I hope I haven't confused you.