To get an idea of the difference between B and L series, take a tape measure & go to the dealership.
When you get there, measure up the front axles on both and compare.
It's just a hunch, but I suspect you'll find the L's have a much beefier front axle.
You may be able to avoid measuring entirely if you can find load ratings for each in the literature.
A stronger front axle means you can lift more weight, safely, with the FEL.
For these smaller 4WD tractors with FELs, the front axle seems to be an Achilles heel, in terms of durability.
Be kind to the front axle and the tractor will be kind to you.
S219 makes a good point about traction, too.
In general, I find that I run out of traction before I run out of power, and our
B2320 &
L3240 are both at the low end of their series for power.
That being said, our land is mostly flat and I don't do as much brush hogging as some others do, so my experience may not be relevant to yours.