Before you connect the transformer to the drives I would check the output voltage because with 70Vac secondary you could get close to 80Vac if the input voltage fluctuates.

Voltage is a key factor in the speed you'll get from the motor, however, the inductance of the motor plays a large part in this so the motor size comes into play.

For instance, if you had 50V and a NEMA 34 motor with say 10mh inductance then the same Nm size NEMA 24 motor with an inductance with only 5mh, this would give higher rpm for the same input voltage.

In general anything above 70Vdc will give a very good performance for a NEMA 23/24 size motor. For NEMA 34 which often has higher inductance then more volts will be required, 100Vdc or more for best performance depending on motor size. For large Nm motors, Mains voltage drives are best.

So with 60Vac after the drive converts this to DC the motor will be seeing aprox 83Vdc which for NEMA 23/4 motors will be more than enough. Also, with smaller motors, You don't want to go too high because you can cause excessive motor heating which is why mike will be recommending on 60Vac even thou the drive can handle 80Vac. Also, it's always better to have plenty of spare overhead so you are not stressing the drive.

I run between 60 and 65vac using a single 625va transformer and don't have any issues. 1000Va is a little too large IMO and you will have a high inrush current.