Need advice on upgrading 2 existing CNCs

At the moment I am running Vexta 2-phase motors putting out about
305in/lbs ea. I believe that they are either NEMA 32 or 34 size. I
have one machine that is a CNC router and the other is a CNC plasma
cutter. I am currently controlling them through a proprietary
control box which also runs proprietary software (I won't mention
who's just yet)

Currently I am only able to reliably run 150-180 IPM before I start
losing steps. I would like to run the machine at 400-600 IPM and jog
around 800-1200 IPM. I can upgrade one of the machines for a cost of
about $7000 that will get me within these specs through the CNC
manufacturer...Is it possible to get this performance at a lower
cost???

My 1st thought is to look into servos, but I have concerns with
there being interference with the Hypertherm plasma cutter machine.
I am also at a loss how to properly select a servo that will be
closest in mounting, torque and target speed. The other option is a
hybrid type stepper like Oriental's AlphaStep or Animatic's
SmartMotor with feedback like a servo.

Can someone tell me if a servo will reliably run on a plasma machine?

What would you suggest, a hybrid stepper with feedback or servo for
both machines?

What kind of ballpark $ am I looking at to upgrade the hardware on
one machine? (Steppers~Servos/power supply/Geckos etc)

Where would you recommend that I purchase my motors to get the best
deal?

Any and all help is greatly appreciated!
Thanks!
-B