To the best of my understanding, these are the distinctions between the 'senior' models in the Ariston range over two decades:
The RD11 is the model Linn admired so much (!) (in production circa 1971 to 1975)
The RD11S has a circular armboard, AC motor & different bearing ('cos Linn had 'won' the patent battle for the conical bearing) (circa 1977 to 1980)
There was a flirtation with an RD11E 3-speed belt driven DC servo model around 1976/7 (came fitted with an arm & had quite different top plate/plinth construction). I suspect the platter & bearing were similar to the RD11. [It has always reminded me, in principle, of its contemporary, the Fons...which probably reflects the common design 'ancestry' involved at this time in their respective companies.]
The RD110SL was a 'luxury' version of the RD11S. It had a Nextel covered top plate, and gilded platter edge. Some were supplied with a solid wood plinth (like that of the later RD90 Superieur) others with a moulded 'non-resonant' dense polymer plinth, which is only distinguishable from the wood version upon closer inspection.
It had an AC motor (some had a clutch, a la Thorens) & I believe the platter was more massive than the standard RD11S (circa 1980 to 1983)
The RD11 Superieur (circa 1983 to 1987) has a metal base, veneered plinth, stainless steel top plate, DC Papst motor with fine tuning pots. for 33/45 speeds. Outboard transformer. Highly modified vestigial subchassis, springs adjustable from above. Fourth spring used to stabilise rotational moments in subchassis to reduce dynamic wow. Single piece machined aluminium platter/subplatter, concave, with threaded spindle for record clamp. Has extended armboard with flange and sabin gasket (but all armboards are otherwise interchangeable)
The RD90 is essentially an RD11 Superieur with an AC motor. Ariston now held the patent rights for 'Q damping' (a proprietary anti-resonance product) which was applied to their turntables from around 1988 onwards.
The RD90 Superieur has a solid wood plinth (of the RD110) massive brass outer platter with fillets of aluminium inlaid to prevent 'ringing', stainless steel top plate, DC Papst motor with external transformer (housed in a wooded case to match the wood of the plinth), brass armboard (more massive to balance the heavier platter), suspension adjustable from above. The spindle is not threaded & there is no concavity machined into the platter (circa 1988 until Ariston's sad demise around 1992/3/4)
This was the most expensive turntable Ariston ever marketed.
I hope that this brief summary is helpful to other Ariston afficionados!
..and if anyone has a spare SME cut Ariston armboard (or could provide a template for one) then I should be eternally grateful...