Just to put this in perspective, my 4x8 foot moving table router had a single NEMA 34 1200 oz/in stepper driving a 700 lb table with a 40mm, 40mm lead, ball screw using a 1.5:1 belt reduction. Would run rapids at 600 IPM max, 500 IPM rapids in normal operation.
The Y axis carriage weighed about 300-400 lb, also driven by a 1200 oz/in NEMA 34 stepper, at a 1:1 ratio, driving a 25mm, 25mm lead ball screw.
I had the micro stepping set up to give 0.0001'' resolution (not to be confused with over all system accuracy which was in the range of +/- 0.001 inch)
Running 5mm lead ball screws implies high motor rpms to get any speed out of the system, which your 1600 oz/in motors are not capable of. The torque is way overkill, you could gear the motor a 1:4 step up (20mm movement/motor revolution) and be OK.
I like the double nut ball screws, but I would have used a greater lead.
You might also look at the Porter Cable 75182 router motor