Hi Pete,

The Video you watched will have been one I made.?
Believe it or not 2 x those motors are now fitted to Harrison M300. They are well OTT to be honest for this machine but lad was in hurry and I wasn't using them at time so let him have 2.

Don't pay too much attention to the speed curves of most steppers because they are done in unrealistic conditions and you will not get 3000rpm from them with 70Vdc. In fact you'll be lucky to get 1500rpm and have any usable torque.
The larger Closed loop motors are still 2 phase motors unlike there better smaller versions which are 3 phase and much smoother and stronger for there size.
Affectively they are just oridinery steppers with an encoder on the back connected to advanced drive which closes the loop much like a servo does. They are better than standard stepper system but not much more powerful and still have the same characteristics in that they start losing torque soon as they turn.

Servo's on the other hand give there rated torque across there full Rpm range and will give peak 3x that for several secs. They also spin much faster and are much smoother in operation. Esp at slow speeds.

Now for your needs you'll get away with 400W servos which are rated 1.27Nm continous and 3nm peak. But Personaly for the small price diffference I'd go for 750w which are rated 2.3nm Cont and 7nm Peak and give plenty of spare power.

The only small down side to Servo's is they require much higher pulse rate than steppers to get there full speed/resolution so you'll need an external motion control card or if using Linux Cnc Mesa card. This however is no big deal because the parallel port is dead and dieing technology so I'd advise you move away from it.
To be honest I'd also advise you to consider Linux cnc rather than Mach3 because Mach isn't great at Lathe. Esp threading.

I'll PM you my number and have chat if you like. (Not tonight thou it's gone 12pm . . Lol)