by floppier i mean its more broken in right out of the box and breaks in faster IMO.
in all honestly, the J3 is only slightly slightly larger, the benefit is that you have fully removable/customizable inserts whereas in the F-3X/F-3XB has sewn in lens dividers on the sides on the main compartment and the end pockets are smaller.
I perfer the J3 just for the fact I can customize the insert configuration with ease.
I regularly carry a 1D2 + 50/1.4 and a Sigma 70-200/2.8, 100/2 or 20/2.8 in the main of my J3 and in the ends 2 space NP-E3s, rocket blower, memory wallet, cleaner cloth.
on the front pocket i carry a 580II and 2 PWs(&cables) or a ST-E2 and that all fits perfectly.
I can squeeze most of that into my F-3X but the issues becomes lense diameter in the smallish sewn in dividers. the F-3X is really meant for older film lenses that are smaller in diameter compared to newer EF mount lenses