Servo motor sizing?

Physical size of a servo motor does it matter when it comes to Nm values,

I am looking at retro fitting a 1997 thermwood router with 3 phase siemens servo motors. The gantry is moved with dual ballscrews driven by two massive servo motors about 330mm by 140mm by 140mm ( Including encoder) specs are 3000r/min 10Nm

One option is these ADTech servo motors rated at 2600w 2500r/min 10Nm cont 25Nm Peak ACH-13260C Middle-inertia Servo Motor | Adtech CNC Europe
130mm by 130mm by 217mm

Looking at the spec these appear quite well matched but the Adtech are a good deal smaller, is this because of the slightly lower rpm rating or just advances in tech between 1997 and 2013?

I guess what I am trying to work out is how best to match old with new and what specs I should be comparing to make the right decision?

Cheers

Size is more down to advances.

I'd guess the old servos will be brushed with pretty large encoders, while the new ones some form of brushless motor with much newer and compacter encoders.