Tell about your experience with your old Audio-Technica SL-1200s..

Yes, pardon me - Technics SL-1200 mkii, but not necessarily limiting the discussion to just that model. 

Fundamental: The plinth, platform: Rock Stability for stylus vibration to go only into the cartridge, combined with plinth isolation from the outside world, as that plinth’s rock stability will transfer external vibration superbly as well.

I strongly encourage you/anyone to consider a table that allows two arms,

Possibly one long, but even two 9" arms has the advantage of having two cartridges aligned/balanced, switch back and forth instantly in a listening session. One fixed cartridge, other removable headshell gives benefits and flexibility.

long arm was my initial motivation, next: one stereo; one mono for Jazz was the real advantage.

Lastly, I went overboard and squeezed a 3rd arm on, so I have MC, MM and Mono. Chakster also squeezed a 3rd arm on that amazing Luxman 2 arm deck, a beauty, (too rare for me).

https://scontent-arn2-1.xx.fbcdn.net/v/t39.30808-6/226605637_6255459961138785_8993343520540965874_n....

Using MM for LP’s I sell (less wear on MC). I just easily changed my MM to a friend’s re-discovered MC so we could hear it, easy as that arm has a removable headshell. Easily compare two Stereo Cartridges, enjoy either’s characteristics.

Removable headshell: consider adjustable Azimuth type, a whole lot easier than shims if a squeak of rotation is needed.

I went vintage JVC CL-P2 Plinth and TT81 Spinner. Solid 7 layer plinth on isoblocks worked for me at current location, I have springy wood floors.

Chakster also squeezed a 3rd arm on that amazing Luxman 2 arm deck, a beauty, (too rare for me).

No, since I have two LUX turntables I got 4 tonearms in use (2 per deck :)

A picture with 3 arms on one deck was made when I decided to swap 64fx with 66fx, so I put the long 66fx near the short 64fx to compare. Love these tonearms!

I had a fully KAB modified SL1200 Mk II and it was a very satisfactory turntable in every way.   When introduced, I bought an SL1200GAE and the two sat side by side for perhaps 6 months, one set up for mono and the other for stereo.  The GAE is sonically superior, more open sounding, cleaner somehow, more revealing.  This difference is pretty obvious on all kinds of music, but was especially easy for me to hear listening to Diana Krall singing and accompanying herself on piano.  Not everyone knows it, but all of Diana's recordings are done live and unedited, meaning she does not do dubs or voice overs.  What you hear is what you get.  Piano is very demanding on vinyl because any amount of wow is noticeable.  This is where some people get confused into thinking direct drive is superior.  Really the most important thing is that the hole is centered in the record.  Generally CDs are better than vinyl for piano, but Sony/Columbia and ECM seem to know how to make superior sounding vinyl records when it comes to piano.  But I digress, both the older MkII and the newer G series play Diana well speed wise, with the G being quieter, cleaner and more open.  Anybody will be able to hear the difference.

Sure they will, you are talking about $400 old Technics (still available at this price) versus $4000 new Technics with completely different motor and superior tonearm and cabinet. No questions that G is simply different class of turntables.