Yes i am referring to the mechbox in your link, and I'd actually recommend either a G&P M140 motor. I didn't notice any speed difference between it and my M120 but I noticed the motor was under less strain to pull that 400fps spring back.
Systema magnums do seem to be the most widely recommend motor, but there's a few cases of people stripping the pinion gear on them. Whether it's due to poor installation or factory defects I don't know.
And trust me, if your re-greasing and maintaining your internals even once every 2 months, having screws you can't strip is a HUGE benefit
