I would think big.. 2ft easily like you said. And again people shouldn't forget to factor in tail size when thinking about max ray size. My tiger is 14" disc length with tail is easily 20"+
I would go for a motoro too as any ray will need a decent size tank and a motoro is much hardier IMO.
FW Alantic Rays stay smaller but totally different look from other rays IMO and long tail again.