Holes in the centerline, the "neutral axis", shouldn't affect the joist deflection.
For other locations you need to find a reference that shows how much E, the modulus of elasticity, is affected by the hole and then do the tedious but not difficult calculations for deflection.
Normal values of E for this wood range from 0.8 million PSI to 2.2 million.
I'll see if I can scrounge up my Strength of Materials text.
There are also patents on a metal sleeve that bolts to joists and allows you to remove a large chunk of the joist cross-section. It works on the principle that steel is about 18x stronger than fir.