So I feel it could well be counter-productive to implement six sigma, if the objective is field cost reduction
Oh, never a truer word.
I think we have now got to a stage where Lean and 6 sigma have merged into a quality monster, that few understand and all fear. 6 sigma means far more than a Cpk of 1.33 to most.
Histrorically it was GE screwed it up in my opinion by refocusing Motorola's ideology of a quality-cetric exercise to a cost-centric exercise. (IMO higher quality implies cost saving / value add).
Today I see it simply as a "toolbox". I simply employ tools such as 8D, 5S (or 6S these days!), measles charts etc when and where they are needed. Common sense must prevail.