Around how many pounds of draw weight does a bow go up when a standard order planed, flat bamboo back is added?

I've never added boo to a finished bow.
Or even a,partially tillered bow.
A guess would be between 10 to 15 pounds.

I seem to remember that adding a back to a finished bow doesn't usually work well.  The belly fibers are already "crushed", so to speak, and adding a backing tends to induce more set and negate any gains.

What kind of wood and why do you want to add a boo backing?

I bought a piece of dimentional hickory, osage handle blank, planed boo back and a strip of black glass for my first try at a laminated bow (Howard Hill style)
I tried to laminate each part in stages due to consequence (bandsaw+palmsander planeing, lack of deep clamps) to name just a few.
I think my second mistake was putting the glass inside the limbs.
It all came apart at the glass last night after stringing it and shooting three arrows.
All pieces are still intact.
It felt very uncomfortable and "stacky" when I was "trying" to shooting it @80#
Gonna try to take out the glass, sand faces and just use hic and boo w osage handle.
I think my first mistake is always patience.

I have added bamboo to a bunch of finished bows. If I glued in about 3" of reflex I would gain 15 or 20 lbs and would need to completely retiller the bow while I dropped poundage.

A bamboo backed former bow becomes a completely new bow. Eric's theory, bamboo shifts the neutral plane of the wood toward the former bows back, crushed belly cells are removed in retillering and you have a new piece of wood to break in.

My #1 bow is an osage selfbow that developed some cracking on the back and need a bamboo backing to save it. Of all my selfbows, it turned out to be the best shooter after backing and retillering.