Congrats, man. That's a good buy you've made. But anyway, the major differences between the S and and RG in the same price range are
22 frets verses 24 frets
mahogany verses basswood
zr trem verses edge pro II/edge III
different shaped bodies
The differences between the S and a SZ would be the
neck scale length (25.5 verses 25.1) and a
fixed bridge as compared to a floating bridge.
But personally, I think you made the right decision. Have fun with that new guitar!