Going by actual PemPro results here, 0.21 seems quite low:
http://www.ccdware.com/products/pempro/examples.cfm
Mind you, the AP mounts listed by Ray are not the current generation. The 900 and 1200 have been phased out - replaced by the 1100 and 1600 respectively. But essentially the same main gear/worm/motor design I think? I'm no expert here...
***4. Count refers to the number of mounts in the sample.