How much of the 20 acres do you expect to mow? And is it a) just keeping the weeds down maybe 3-4 times a year, b)grooming a pasture with regular bush hog mowing or c) turf-type finish mowing?
The
L3400 is just big enough to run a 6ft bush hog type mower or a 7ft finish mower, which are probably the smallest you would want to use if you are cutting more than, say, 10 acres. The MX5000 would open the possibility of getting a smaller wing-type mower - around 10ft cutting width - that could dramatically reduce your mowing time, although batwings are expensive.
On the other hand, if you will only be mowing a few of those 20 acres, you might appreciate the smaller size of the
L3400.
Regarding the FEL, the Kub loader for the MX5000 has a much larger capacity than the one for the
L3400, but you would be handicapping its usefulness quite a bit with a 2WD machine, even with plenty of weight being added in the back. The issues are traction and front axle capacity.