In case you don't get a better answer, then I suggest this:

About 3/8" (each direction) is usually enough without being too much for that size plane. But to make sure you can control it, I would set up my high rates to move about 5/8" or so in case the 3/8" isn't enough.

Hopefully you get a more definitive answer, but it will help if you post the specific model you have. Also, check out the manufacturer's web site for info or to contact them directly.