I need some help with servo's PLZ!!!! RETROFIT

I thought a 600in/oz servo with 900rpm would have enough power to run
my Knee mill. The individual I want to purchase a drive kit from
does not agree with me (AHEM Camtronics) My table is 30" x 15"
already running a cnc control that i am removing (don't ask why) The
current motors are 500in/oz and 2000 rpm, i'm not concerned about the
rpm because the spindle speed is going to restrict the feedrate.
Additionally the 600in/oz motors would be running from gecko drives.
How can i find out if this is enough servo or not, also let me know
if this setup will work. This mill is a Shizouka with ballsrews.