I fail to see how the equipment a diver is wearing contributes to his/her ability to dive safely when it comes to nitrogen narcosis. Certainly if a tethered diver ran into a problem, he could be removed from the hazard. On the other hand, being in communication with the surface allows the diver to be monitored. There was obviously nothing experienced by the tender that would have lead him to suspect that I wasn't safe, or the dive would have been immediately terminated. Also, there was never any indication that the quality of my work being performed was sub-standard during this time period. I suggest that this is suitable evidence that I was able to perform complex tasks at depth while breathing air at depth. Thousands of commercial divers do this daily.
The only dive I terminated on air resulting from narcosis, was one that I did to 250'. As soon as I noticed that I was starting to experience some difficulty with direction, I terminated the dive. I was using scuba at the time. Nitrogen narcosis isn't the Boogie Man. You can feel the affects build and can terminate the dive accordingly.
To answer your question, of the commercial time I've listed, only about 100 hours would qualify on scuba over 150'. Although I haven't checked my other logs, I suspect that I could add an additional 300 recreational hours and another 200 hours with the Navy to this figure (scuba breathing air over 150'). Considering my years at DCIEM as a test diver, there would be a considerable amount more time to add, but that's not with scuba.