Well like I say with those 50Vdc drives then you really don't want to run much above 45Vdc, I certainly wouldn't run them at 48vdc because it's like playing Russian roulette.

I would build a PSU using a toroidal transformer rated at 500Va with 30V secondary outputs wired in parallel. This will give you approx 43Vdc and 16A but usually, the incoming mains fluctuates anywhere between 230Vac and 250Vac so in use you'll probably end up around 45Vdc.
If you know your incoming voltage is stable and 230vac then you could go with a 32Vac transformer which will give you 45Vdc. Personally I wouldn't because a few less volts won't make a big difference to the speed but certainly will blow a drive up.

Now regards the speed and running at 3200 resolution, by which I presume you mean micro-stepping.? Then first off I need to say that Micro stepping shouldn't be classed as resolution as that is a function of the ball screw and micro-stepping is more intended for smoother running of the motors. However, because of how steppers work there is a limit to what is useful and usable. Most steppers can't resolve down to high micro stepping levels and 3200 is about at the Max that is useful.
Now the side effects of running at this level of MS are lower torque and much higher demand on the controller. For instance, you'll double the amount of pulse frequency required for 3200 than 1600 but have less torque with very little gain in motor smoothness. If your motion controller is limited to say 25Khz then this will half the velocity, so it's only worth running at high MS-like 3200 if you have an excess frequency in the controller.
1600 Ms is more than enough for any stepper system and doesn't tax the controller.

Now with those 2 phase closed-loop steppers and 45Vdc you'll get around 900Rpm that is usable and will max out around 1200-1300Rpm before stalling.
So with 5mm pitch and 900rpm then provided your axis are not binding or sticky and the gantry isn't silly heavy then your Max velocity will be around 4500mm/min and you may push it just above 5000mm/min.
A realistic MAX cutting velocity of 4000mm/min is about what I would estimate with those motors/pitch and voltage.