Back to your mechanical reduction, another option you have is new pulleys. On a few routers I've retrofit to cut aluminum I've even gone as far as replacing the pulleys to get better mechanical reduction as it's the easiest and least expensive way to get in that "sweet spot". It does not appear you can go any larger on the driven pulley (maybe a few teeth?) but you could get a smaller drive pulley to help. Not sure of the bore size on your pulley but even going as low as a 14 or 15 tooth pulley would get you in the 4:1 or higher gear reduction range. This would help when using a router as a mill.
![Very Happy :D](./images/smilies/icon_e_biggrin.gif)
I do use Clearpath servos on my retrofits and use a higher steps/rev as well when building machines to cut aluminum or acrylic.
Lastly, have a closer look at the rack and pinion, depending on the age of the machine you might want to, at the very least, make some adjustments. Helical rack and pinion are far better than straight gears but I'm guessing this machine has straight gears.