Forks can vary vastly in stiffness whilst having the same stanchion diameter – lots of variables including lowers, bushings, arches, crown, steerer, dropouts, axle and of course the wall thickness of those stanchions. I think I’d go for a BFe. If you were the same weight but shorter and therefore on a medium it would be a very difficult decision!
The Float 140s aren’t super stiff but they’re not that noodly – with some fairly stiff wheels it should batter through the rocks with impunity.
Regarding the geometry working well with various fork lengths – as you lengthen the fork you raise the headtube, slacken the head angle, shorten the top tube, raise the bottom bracket and slacken the seat tube. All this makes the frame better at going down the rough stuff, apart from the BB height issue which is more contentious (reduced pedal strikes in the gnarr, greater ease of manualling, but less stable). I believe the Soul was originally designed for a 100mm fork despite many claiming that 120mm is the ‘sweet spot’. Basically changing the fork length manages to change the whole character of the bike in a remarkably cohesive way.