Hi MrCynical, I know the sets you mean - they are the same recordings (afaik) but they are on DG though (not decca)

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I have the box set of the full Mozart symphonies (in the incarnation below) and can confirm that it is a very nice set - lively performances and great sound, especially considering the vintage of the recording!.
I must admit that I havent been compelled to re-visit the earlier Symphonies again but they are nice to have as a reference, I think you will not regret getting this set whichever version you choose

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