Your 425 oz/in motors should work fine on your SB1001. Assuming the 570 oz/in motors have a higher Amp rating than the 425 motors, you could get the larger motor for the Z-axis and run it using your current control settings. If you wanted more power in the future you wouldn't need to upgrade the motor.

I picked the 570 oz/in motors for my lathe as that was what was on my G0704 mill and it allows me to use the same control. Initially I thought it would be overkill, but after a year of running it a few hours a week there haven't been any problems. On the Z-axis of my mill I have a Nema34 1200 oz/in motor... which replaced the first 650(ish) oz/in motor I tried. My control has a 48v 6.7amp power supply for the 570 oz/in motors and a seperate 60v power supply for the Nema34 on my mill's Z (another later date upgrade).

Hoss Machine's page on the G0704 electronics gives the best writeup I have found on the electronics end. In retrospect the 3-axis digital driver would probably be a great choice for my mill and lathe. My mill's Z-axis runs on a digital driver and it runs much quieter than the Keling analog drivers. I've also dumped any desire to run my machines through the parallel port of an old Dell computer. Getting an Ethernet SmoothStepper or UC100 lets you use a modern laptop computer and you won't have to upgrade later. The best way to save money is to buy the right thing the first time!!

I'll post some pictures of my control sometime next week.

Anyway, short answer is that your 425 oz/in motors should be fine for both the lathe and mill. With these bechtop machines a lot of getting good results is figuring out how much slower you have to go than on a full sized machine.

South Bend SB1001 8K Lathe CNC