There was some advice from Cy (of Cotic) about this over on STW.
He said that the shorter the AtoC (clearance allowing) was the best way forward.
A AtoC of 425mm is closer to the geometry of an 80mm fork.
I have a Salsa Cromoto on my 63mm travel adjusted frame and that works fine with a 29'' wheel - maybe a bit tall but not so much to be a pain - about the same as it was with 100mm forks on.
I would have thought that a 440mm fork and a 29'' wheel would jack up the front end on your bike too much
May not though
440 is roughly about the same as a 100mm fork and the Soul is designed for a 120mm fork but works really well up to 140mm. The Bfe which shares the same geometry is designed around anything up to a 160mm fork so there is room for manouvre.
Depends on the frame, going slacker is no crime and all the rage with the kids. I'm running a 170mm fork on my Banshee (designed for 140-160mm).
I would worry about toe clearance more than head angle tbh.