Lemme get my oar in...
On a very good rigid 12x24 lathe, chicom, chester crafstman, bought new from chester around 2007 perhaps..
it is likely the most "cnc" shop built lathe in the world.
At vast cost, changes, tests, hw, hours, etc etc.

The original spindle was 1.5 kW AC 220V.
And really worked well, had excellent torque, could do blue/black chips on 200 mm steel discs for hours, at 1-1.2 mm DOC.
Note its 200 mm D, at 1 mm doc. About 200 rpm afair.

I put on a servo.
AC brushless, 220V (50 hz, spain), 3000 rpm max, 10.000 counts, 10 Nm cont, 30 Nm peak for 3 secs.
Very good mount.
Ie very rigid, 30x40 mm frames in tool steel.
Motor mount plate 250x200x20 mm tool steel. Etc. About 50 kg in mass.
IE very rigid.

8 mm profile, HTD belts, 24:72 so 1:3 drive.
30 mm wide. This is important.
Taperlock pulleys.
Gives me 0-1000 rpm.

The setup gives me 90 Nm torque, 0 rpm to 1000 rpm.
And 0.01 degree indexing, c axis, +/-. 30.000 /rev.

For comparison, a 10 kW HAAS ST10, 50.000€, gets 102 Nm max at 1200 rpm.
And quite a lot less, at lower revs.

The motor is silent, belt has some noise.
Lifetime should be about 10k hours - industrial.

I was always of the opinion that I had more than enough torque.
Now I have much more, and I find it wonderful.
I was wrong.
Much more torque is extremely useful. Extremely.
I don΄t exactly know why ...
and I am pretty sure that this works so well because my lathe is very short/heavy for its size, and thus very rigid, for its size.

Variable-speed 0-1000 rpm, perfect speeds, perfect surface speed, is great.
Zero belt changes ever (could add pulleys, at need - if I made small sub 10 mm steel parts- I dont, so far).
--
Good 30 mm wide belts and pulleys cost money.
About 300€ to me (some spares).

Making a big heavy frame is not difficult, but is hard work, heavy, expensive parts, lots of hours.
Servo set all in 1500€ at 22% VAT in Spain - I am a wholesaler/importer.
A 3kw+ servo maybe 2500€.