The Rosta parts are DR-A27X100 BR27 & WS18-27
If your cutting at 380 ipm then I would aim for a max of at least 500 or 600ipm.
Commercial plasma machines run around 1000ipm max.
There is an industry standard that it is considered normal to keep the inertia ratio of the motor to final load to under 10:1 the deciding factors are motor, all gear/speed reduction components, the weight of the final load and the acceleration required.
It is a good idea to obtain one of the free motor sizing software's available from many of the motion/servo motor manufacturers and play around with it, plugging in various numbers. One of those is Kolmorgen
http://www.electromate.com/technical...morgansoftware
There are others, this allows you to get a feel for what you are looking at for final sizing.
Increasing your reduction ratio greatly improves your inertia factor, but if you go too high, you will need a very high motor rpm to get the max feedrate you want. To grasp the effect of inertia, Imagine cutting a square at 380ipm with a 200lb gantry, the Y axis has completed it cut, now the 200lb gantry has to immediatly travel at 380ipm in the X with, ideally, hardly any visible sign of acceleration.
Al