I use none of those settings, that is why I've never been to a chamber. The only time I reach 1.4 is at gas switch in deco or MOD. When diving Nitrox I make multiple dives and high PPO2 is cummulative.
1.4 for working part of the dive, 1.6 for the deco. If it was a dive in UK waters that may be challenging at 6m, i may work off 1.5 on deco just to be cautious.
Depends on your profile. If multileveling it, then 1.4 max. But if you are maintaining a constant depth, then consider 1.2 to 1.3. The objective of nitrox is not to get the highest ppO2, but to use it as a tool based on your profile.