ANStructs

OP is short for "original poster" IMO is short for "in my opinion" 🙄

I assumed by this question, you meant to ask the following? Answer: Using FEMA guidelines? I take that you're performing the "Performance based design" of a structure. If so, then since the performance limits specified by FEMA (i.e., IO, LS and CP) lies within the zone "A-B", AB is the zone that should most accurately define the hinge rotation capacities of your joints, anything beyond point B will not be used. You can check the moment curvature curve of a section in the section designer if you're using sap2000 or Etabs. Note that the ultimate rotation obtained from the ultimate curvature of your provided section may be more than the rotation specified by FEMA. FEMA values are based on research, however, it allows you to use different values "if" experiments shows that the provided rotation capacity is indeed more than those specified by the code. I'll advise you to stick with FEMA values because they most likely take into account the additional rotation due to shear cracks and rebar slips, which the M-phi curve from the section designer does not consider in it's calculations. It goes without saying that, you should make sure that the provided rotational capacity is not less than the one specified be FEMA.

I agree with the point made by SMAQ. Although, analysing the frame with pinned supports will be on the safer side as far as the design of frame is concerned, but the same could not be said for the foundation. The design of foundation will most definitely govern for a "fixed base support" model. Not to mention, the hinged base support detail at column-foundation joint, is not a preferrible joint detail for "code" desired sway mechanism for a moment frame.

First of all I'm having difficulty in understanding what does the OP mean by extra bars? IMO the actual curtailment of rebars should be based on the moment envelope and the required development lengths.