The amount of production that should come from hygiene all depends upon the production of the dentist and the type of hygiene care delivered.
I have one client who produces $5000.00 a day. His hygienist produces $1200.00 a day. Another client produces $2200.00 a day. His hygienist produces around $1000.00 a day. Different treatment protocols and their definition of "ideal dentistry" and "ideal hygiene care".
What would be a good amount of production for a hygienist would be based upon the fee schedule in the office adding together the actual cleaning price, x-rays and what that would come out to hourly amount.
Most offices do x-rays once or twice per year and a full series once every five years (this is usually based on what insurance companies allow - I know it sucks to to be told what to do by insurance companies).
The ones that do x-rays every six months would have the higher daily average as x-rays done by the hygienist is counted towards their production. The doctor exam is usually not included in their production. I have seen some doctors that count the exam towards hygiene production. Not smart but not uncommon.
Offices that do root planing and scaling on a much more frequent basis have much higher hygiene production averages. This, of course, depends upon the doctor's viewpoint on what the hygiene department should deliver. So depending upon the type of hygiene a practice delivers I look for what a practice can optimally produce based on the type of services they offer.
I would be more concerned about the amount of "open hours" in hygiene. An open hour would be when they are paying the hygienist without delivering services due to cancellations or unscheduled appointments as obviously there is no production going on. The first client I mentioned above, for example, has less than five "open hours" per month with two hygienists. Some offices will have five or six hours per week open! Now that really hurts!