I have Salsa Short 'n Shallow bars as well. I don't know how narrow they are, but I know my bars look tiny compared to everyone else. I can't recall having arm pains, my shoulders and arms feel nice and relaxed on my bike. Yellow is right, I can't imagine putting anything other than a computer on my bars. It already seems like such a tiny space between the brake hoods.

If your new Salsa bars have the ergo bump you are lucky! Once I figured out it was there riding in the drop is so comfortable.