All things being equal, the Cl emulsion will be slower with greater contrast. You might also get a bit of peppering (spontaneously developed grain.) Chris's goal is to go as natural and close to the ocean as possible. He celebrates the slowness of the emulsion. He figures (and I agree) that there are fantastic, fast, panchromatic films commercially available. Recreating them is not his windmill. He loves the effects that come from slowness and colorblindness.
Re ammonium chloride: I don't know. My philosophy is 'give it a try' (maybe after you try sodium chloride.) Use a little less. The reacting amount of KBr to one part silver nitrate is 0.7. NH4Cl and NaCl are about 0.4. The advantage of using an ammonium version of a given halide is that's a mild silver solvent. You'll be less likely to get peppering. Ammonium chloride is the usual halide in printing-out papers, but usually with silver in excess and with an organic acid, so I can't see that you'll get funky negatives with a dry plate recipe's ingredients and proportions.
Luck and fun