The SA site
Spare Air Models - 300 Standard & Nitrox and Model 170 plus Part and Accessories says that their 3 cf holds 85 liters @ 3,000psi, so on your chart it would be good for a bailout from 26m/85 ft.
That's dependent on the SAC that you use. As mentioned already on the thread, it would be imprudent and unrealistic to expect a normal SAC in the event of sudden OOA emergency at depth.
SA seems to have stopped making the 6 cf, the only possibly reasonable model they had, but still - the one we are discussing here - and I presume it holds 170 liters @ 3,000psi, good for bailout on your chart from 40m/131ft. For leeway, one could still finish with a CESA.
Again, dependent on SAC and no delays in ascent. Prudence demands the expectation of a delay to ascent, especially at deeper depths.. which is why 'Rock Bottom' always includes a 1 min 'fudge factor' at depth.
There's a factor of time allocated to 'shock'....."waaaah!"
Then another period allocated to 'emergency recognition'.... "why can't I breath? ... thump the regulator...check the SPG... that can't be right... how can I be out of air?"
Then there is 'denial'... "this can't be happening... it can't be happening to me..."
Then there is 'acceptance'...."I need to get my act together... or I might die today..."
Then there is 'problem solving'... "how deep am I? what resources do I have? what did I learn in training?"
Then there is a 'first reaction'..."where is my buddy? I can/cannot see them... can I swim to them? Can I get their attention?" [tries to get attention...fails]
Then there is a 'resolution'..."I need to ascend.... I need to use my Spare Air now".
Then there is 'preparation'.... [deploys Spare Air]
Then the ascent happens....
... in reality add "gasp...gasp....gasp" of stressed breathing throughout the duration of this....
... for some divers, the response to any of the above phases could lead to panic - Spare Air would be forgotten anyway...
For the SA to have any relevance as an emergency ascent device, the diver would need to make an instantaneous decision/reaction to ascend. My opinion is that possession of a SA would actually delay that reaction - unless the user was meticulous in drilling and rehearsing an ingrained OOA reaction, specifically utilizing the SA. From experience, the sort of diver who would have that meticulous, preparatory nature is not the sort of diver who'd either need, nor rely upon, a device like the Spare Air.
Yes.... in a perfect scenario.... the diver would instantly recognize and correctly respond to an OOA... immediate uncompromised ascent, deploy Spare Air on that ascent... regulate a slow, calm breathing pattern throughout the event.
How many divers would realistically be able to ensure that 'perfect scenario'? Are they the sort of divers who'd rely on a Spare Air?
The most critical factor in a diving emergency, especially OOA, is TIME. Gas gives you time. Time to think. Time to react. Time to regain emotional control. Time to plan. Time to problem solve. Time to ascend.
Spare Air doesn't give you TIME... it just supports an immediate ascent, that has to be done perfectly, first-time, no errors, no delays.