The methods described in your link from Oriental Motors are essentially the same as my script here. Mine is a bit more detailed in some areas, for what it's worth...It's also to get a qualitative feeling for the system.

If you don't have the torque speed curve for a particular stepper motor, a reasonable assumption is that it outputs 2/3rds of the rated holding torque up to the corner speed, then assume constant power from that point. This is essentially the method used in Irving's spreadsheet. This is of course an assumption, so it's safest to design for just below the corner speed, unless you're very confident about what you're doing. I guess I could add a plot of the stepper motor torque speed curve and machine torque requirement to my scrip, then look for the intersection to find the maximum speed... but nobody seems interested.