My subjective opinion is based off of how I’ve felt in the past being narced between 100’ and 165’ with and without helium. 165’ is TOO DAMN DEEP. At 100’ I am aware of the narc but not particularly concerned. 165 is my deepest without helium and I’ll never do it again, I’m glad to have done it once to actually know what it’s like and why it’s a terrible idea.
Objectively , the only thing I have is gas density issues setting a limit which coincides well with my personal subjective limits. Just because I have those limits does not mean I spend my time chasing depth, my limit is a hard limit I won’t cross without helium and usually my CCR. I avoid approaching my limit without a good reason. I’m not going to pretend I can objectively measure narcosis, that I’m somehow immune, or that I have a tolerance; no one has done an adequate job quantifying narc analytically as far as I know therefore anyone’s depth limit based off of narcosis is inherently subjective.
TL/DR, I am on team helium but I find the 100’ limit overly conservative.