You really want to go for 8 or 10 microstepping, not sure what your drives will allow.
Ok so say you can change to 10 micro steps that would mean your steps per unit would be
10 x 200 = 2000 per motor rev
2,000 x 2.5 = 5000 per 5mm so steps per unit would be 1,000
Try an Vel of around 2,000mm/min and an Accel of around 50mm/s/s and see how you go.
If you set to 8 microstepping then your steps per unit would be 800
Hood