I have a X-55 and the softest spring and no curve for either the Spit or the Stang for the exact things Zach mentioned. With the soft spring I don't suffer the infamous dead zone a stiffer stick would produce and I prefer to work my muscle memory with the original setting of the plane.
I find the Spitfire very easy to turn in normal flight (say 200mph @ angel 10), with a well trimmed aeroplane you don't even need rudder input when banking, the needle stays in the middle!
Obviously, when dog fighting or flying aggressively, rudder inputs are needed but I find too that when you bank the plane it tends to lift the nose up so you have to adjust with the stick. Should I use the rudder instead to turn and then adjust my attitude with the stick instead?