There are many variables and the whole deep air performance issue is dynamically complex so it is hard to make any absolute statements.
In general, divers who dive deep air tend to work up to greater depths over the course of a few weeks. In my experience, a deep air dive early in the season generally leaves me feeling less confident and on top of my game than one late in the season so there is an effect there, but I am not conviced accommodation to higher narcosis levels is the cause. Early in the season I am knocking off the rust from a few months of not diving, and I feel less on top of my game even on shallow dives where narcosis is not a factor so it's the improvement over all that helps not a better accommodation to narcosis.
Also, I have been diving for a quarter century and have something over 1500 dives in a wide varierty of environments and in some very demanding conditions (cold, zero viz, strong current, etc). I also tend to be a thinker and will consider and run through possible scenarios prior to dives. The end result is that the normal demands of diving (bouyancy, checking the SPG, depth, etc on a regular basis, noting navigational landmarks, being aware of possible situations that may involve more risk, entanglement etc, are second nature and/or my response to situations that arise is well drilled with a great deal of prior experience to draw on so there is more cognitive ability left over to deal with the surprises or unique problems and threats that may arise on a deep air dive. A new diver who is highly task loaded with the basics and/or a diver encountering a new situation for the first time, may require a lot more resources to properly identify and work the problem.
People also vary in the cognitive ability they start with as well as in their ability to multi task. I am a good instrument pilot in part because I multi task very well while maintaining the neccesary focus on the overall situation and that same trait helps on deep air dives. Not all people multitask to the same degree. Women are reported to be better at it on average than men but the variance within those groups is greater than the variance between groups so being male or female carries no real significance for the individual diver.
CO2 retention is associated with more severe impairment by narcosis as are rapid descents, so dive bombing to the bottom and then skip breathing to extend your gas at the bottom may potentiate narosis and may be counterproductive.
All of the above I think also explains the wide variety of opinon you get. Some divers are very comfortable on deep air and they tend to also be the divers wh know their limits on deep air and have the judgment to stay within those limits. Other divers may take a sometimes extreme view that an END greater than 70', 80' or 100' is tantamount to playing russian roulette. Still others claim that deep air divers remember very little of the dive. I have never encountered any notable problems in the area - I may or may not be forgetting more, but I think the important issue is does a diver recall enough. In any event I see need for 30/30 in my diving future.
I have seen divers struggle with things like operating cameras below 100' on air, but usually when you follow up with them, the camera operation is not second nature to them at the surface, so it's not surprising that things get so bad under the effects of narcosis that they don't operate it effectively. In effect, narcosis makes existing problems or weaknesses worse, so eliminating those weaknesses in the first place is a good place to start if you are contemplating a deep air dive. If you see some guy in the park with a housed camera and neoprene gloves taking pictures, it is quite possibly me getting refamiliarized with my camera before a deep dive.
The demands of the dive are important as well. I would consider doing a deep air dive to 165'-180' to explore the exterior of a wreck in an area where visibility is good, currents are not extreme and where hazards such as fishing nets are minimal, but the more of those factors you add back in the shallower I want to be or the more helium I want to add to the mix. When you start talking about pentration of an unfamiliar wreck, you are getting into iffy territory with regard to deep air.
Narcosis also seems to potentiate any existing mood. If you are euphoric at the surface narcosis will porbably make it worse. If you are normally anxious, a dark and scary dive below 100' may greatly increase your normal level of anxiety. At a personal level that may mean some people are just not good candidates for deep air. For any diver, if you begin to feel too anxious and are out fo your comfort zone, abort the dive and that advice transcends the mix you are on or your END.
