z63 is definitely softer then 63x. I think its a pretty good all around string. Not much repulsion or quick bounce you get from a typical thin string but theres a good amount of shuttle hold. I found power transfer from smashes pretty easy and powerful. I would say in terms of soft feeling its around ashaway level and in between yonex soft to medium.
z63x if you want more pingy, louder sound and better bounce on contact with shuttle this would be for you. To me I wasn't really impress, just seemed like something I am already use too from other strings. Good competitor to exbolt 63.
z58 is still my go too, can get the performance and feel at a lower tension then 63x and with them being cheaper then Yonex strings it was a no brainer. I also don't really break strings and all of them are were very durable to me. 63x however feels it has a longer life and playability.