>There is also a significant variation in how the same person performs across multiple tasks.
Not only that, sometimes one individual can engineer things 10X better than at other times.
>Do these two engineers have the same experience with the technology at hand?
No, one has 10x the experience.
>How familiar are they with the system they're working on?
Very, one is just 10X more familiar.
>Do they have the same ability to make decisions on the go?
No, one is a 10X better decision maker.
>How easily can they get help?
Both easily, but one of the two only needs help 10X less often.
But practically does it really matter?
Even if we knew the case, one can't just e.g. whip 0.4x into 1x, so a 2x remains a very valuable 2/0.4 jump.
This is pure speculation, which is why actual data would be useful. Is a measured 0.4x performer that way for innate reasons or is that something which some combination of training and mentoring, better tools, streamlined environments, etc. can help with? — or is the way that's measured even valid? I've seen a few cases where someone got flack for being slow until wider perspective showed that they were the only one solving the customer's real problem because it turned out that what they were doing was more complicated than it looked and/or the other guys were “solving” it in ways that required lots of ongoing maintenance.
For this or that individual (as per your example of "a few cases"), maybe.
For the majority do you think there will be something that hasn't been tried until now, what with all 2000 methodologies of management, team structure, company culture, development methodologies, tooling, agile, waterfall, and what have you, that will suddenly make a difference?
Performance is relative, so if the norm is 0.4x, that's the actual "1x" base to just 10x programmers by, even if it's below what a 0.4x programmer could potentially achieve if they really tried.
In other words, if most devs are underperforming due to complacency, lack of motivation, etc., that should also factor in in the 10x programmer calculation.
So, 10x doesn't have to be "10x as good when both are 100% motivated" just "10x as effective" is enough (even if it's because they are more motivated and not actually more intelligent, knowlegeable etc).