I've got an '89 4003S and a '93 4003S/8, both with the big fat horns. I like em. Both these basses have very stable necks. I often wonder if the slight extra support provided by the extra wood has anything to do with that? My other Ric is a '92 4001CS with skinny horns. That neck is more prone to movement, but it's also much thinner (front to back) than any Ric I've ever played, particularly in the upper registers.
Besides the new horns being pretty skinny, they also shifted the wings back slightly, so there's hardly anything between the pickguard and the edge of the body where the neck meets wings on the treble side. Sorry for the run-on sentence, and I hope that makes sense!