I use 23s X 1 in. for every thing including the pecs.
I usually stick the upper outer pecs going in at an inward angle. Never strait in. I will also sometimes stick my upper middle pec areas in the same fashion. At an slight angle but still deep into the muscle. If this will be your first pec injection i suggest that you do not go over .5 c.
If you do get ready to "reap your reward".