I have an 18'' marley and it's spot on for me with a 60mm stem at 5' 7.
It builds into a light and very capable bike. I have never had a sprightly lightweight steel frame to compare the stiffness of it to but it seems fine and not overly tiring. I have had numerous long travel hardtail frames (chameleon,stiffee,surge,mmmbop,BFe) and along with the mmmbop it's definitely the best handling of them all. As said previously its slack head angle helps on the downs but it has a relatively steep seat angle to position the weight to stop the front wandering too much.
Something to think about would be the length / travel of fork used. 140/150 would be ideal with a ragley. But having had a BFe, which has I believe the same angles as the soul, I don't think 150 would feel very good. 150 on the BFe made the seat angle very slack and the front wander very easily. You can compensate with technique but it's not ideal. Probably around 120 would be ideal with the soul.
I imagine the soul would build into a lovely bike but also the ragley manufacturing has improved to say the least. The paint / welding is miles better on the marley over the mmmbop.