I have both, and they sound, play and feel nothing like each other.
The 594 is the very best guitar made on planet earth. It feels, sounds and plays like no other guitar ever made. The 58/15LT pickups are clear, transient, split incredibly well, and they can drive as hard as you like with any channel or boost of your choice. The pattern vintage neck feels like worn in blue jeans. The bridge feels like a rock hammock under my palm. I can play anything on it and feel like a god.
The Special SH is a wonderful guitar. The 58/15MT pickups are more mid-range compressed. They sound good, but not as clearly as the LTs. Mine has a maple neck and Korina body, which I’ve learned I hate. I’d love to play a hog version to compare. Truth be told, I never play it. Which is sad, because I upgraded the pickup rings and buttons to flame maple and it looks like a Private Stock. Just sexy.
To each their own, but if you don’t have a 594, I believe your quiver will only be lesser for it without one. It is by far the most glorious rock machine on terra firma. Hands down. The discussion is over. Just f&cking crazy good.