Looks like some beautiful property--congratulations!
Most folks will tell you to buy bigger than you think you need right now, as there are fewer regrets over having too much capacity than not not enough. I think that's sound advice in most cases, especially when you may not yet be able to envision all the tasks you'll want to pursue.
That said, for me the BX is the ultimate mower and firewood hauler--my two main uses. It's small enough to maneuver in tight spaces and not take up too much space in a garage; light enough not to damage the lawn; and has great stability and traction for use on slopes and hauling wood carts. The FEL has all the capacity I've ever needed for moving gravel, snow, mulch and wood. Ground clearance has never been an issue.
For me, my BX's limitation is in the amount of rear PTO horsepower and lift. My 1870 can and does run a smaller chipper/shredder adequately, but a larger capacity would be nice there. And I sometimes would like the ability to run a 5' brush hog or other rear mower, and that's more than my machine can do. So I occasionally find myself looking at the specs on the B2650, but overall, I still think I made the right choice for my situation, especially when my finances are considered.
I don't know squat about flail mowers, but in addition to making sure you've got adequate PTO horse power for the mower width you want, make sure you've got adequate lift on the three point hitch. Will you be using it to mow lawn, or will that chore be covered by a dedicated mowing machine?
