IMO the Rattler is way more stable than an 86 Softie. The 86 was a super-duper touch disc. I couldn't throw one to save my life. I could use a Rattler on a short drive or long approach; it was stable enough to throw. An 86 Softie when I put any power on it at all would turn and burn. I can't really think of any current disc that reminds me of it.
That and the nipple is on top. Who thought that was a good idea? They were next to impossible to spin becasue you couldn't judge the center of the disc by the nipple. My pre-putt is always standing and spinning the disc while waiting my turn, and the 86 Softie would screw that up. It was a really frustrating disc for me. There was a guy from Peoria that was a really good player who used them; he won AM Worlds and was a solid pro for many years after that. Scott Martin? Anyway, he used to come down to St. Louis and beat up on us putting that 86 Softie, so I knew that if you figured out the touch with that disc it could be deadly. I stuck with it for a couple of years, never did figure out the touch.