Micro Seiki, or TW AC-1

Maril: I can't answer your question, because I have no hands-on experience with either table. I'd also ask about the 8000, and there are a few owners of both Micro Seiki tables here who could tell you the differences. They would seem to be tweakier but you are probably prepared for that.
I'm bothering to comment because we share similar systems in fundamental ways. I will tell you, without shilling for the table I use, that a heavyweight table, set up properly, seems to disappear and the faint 'halo' that people seem to associate with vinyl playback, pretty much disappears.
I also have an SP-10 (albeit a Mk1) that I have owned since new, but hasn't seen use for decades; I'll probably revive it someday. I'll be interested to see responses, particularly from those who have hands-on experience with BOTH tables you mention, because I'm sure each has a loyal following.

Whart,
Thank you for your response. Our systems are indeed very similar.
It's so happens, that I know owners/ designer of your Veloce linestage. They are both members of our Philadelphia Area Audio Group.
One day I will try to arrange an audition of Veloce in my own system. I heard it many times at various shows, but in the context of unfamiliar system.
Anyhow, back to our sheep, I mean turntables.
I completely agree with you about the "heavyweight" turntables being a different animal, compared to my DD Technics, and that's the main reason, I want to try one in my own system.
J.C. Verdier Platine seems like another interesting choice, as well, as Transrotor tables with magnetic drive, and Kuzma.
I'm a little leary about heavily investing in a 25 y/o Micro Seiki, though they have a great reliability record, but with the company being defunct, one is left to a mercy of random suppliers, or DIY in case of malfunction.

I have a friend with a Micro Seiki. Wonderful table but it does need tweaking and labor - almost constantly. He has the table down well over 50% of the time as he waits for parts, etc. Finding parts are becoming an issue for him.

The TW AC-1 is a table that I own (owner discretion here!). It is a fantastic table. Labor free once set up. It is a high mass table, tons of tight deep bass compared to my VPI Aries 3 I owned before. It is also very delicate and incredibly detailed. I love this table and you can always upgrade it with extra motors, tonearms, feet, etc as you would like.

Highwater Sound is the importer for TW Acustic in the US and are fantastic to deal with whether you purchased new from them or bought used. TW is a great company and are always back-ordered, so their business is strong.

Don't see how you could go wrong with a TW AC-1.

These turntables show indeed huge differences in Performance, but it depends
on knowledge of the owner (perfect reproduction of the sound of real music
performed in a real space or: "good" sound is whatever one likes)

Micro Seiki
5000

The Japanese made more right 25 years ago than most Manufacturers today.
Together.
Very reliable, no coloration, adjustable motor, but some care is needed when
buying one, some owners have the remarkable ability to ruin everything

Platine
Verdier

That is an original one from the 80's with Magnets from France, a Legend in
Europe, sonically really outstanding, no longer available in that configuration

Kuzma XL

Was compared side by side with a Seiki 5000, after 5 min. the owner made it
ready to sell...but overall a good Turntable

Raven AC

Like a Linn LP12 but "in black & heavy"
No matter what you do, it will sound always different...great for Reissues

Kuzma 4P

Soft dynamics, great compensation for very analytic sounding Systems, here it
is used with a Raven AC from one of my friends.
The pic is a bit old, a new one would show a lot of dust onto, the user doe not
use it anymore ...left side is a Kuzma Airline

As you have a Porter plinth and Albert's former reference arm, the SME 312S, you may want to check out his latest comments on his system page about his new tonearm. It may change your bass performance.

I would also think you could add some superior isolation like a Vibraplane to your existing table and hear quite an improvement. This would cost you much less money and you could always use it under your next table to which Syntax could attest.