Watching this with interest.
This is quite comparable to "upgrade" of M52 to M52TU.
While M52TU is lighter due to the introduction of aluminum block (vs iron on M52) and more efficient due to several "improvements", the fact is that M52 will easily outlive M52TU and it's more reliable.
The little I know about M57 vs TU, it does seem like a similar story.

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2010 BMW M6 * Black Saphire Metallic * Full Black Merino Leather
2019 BMW X3 M40i * Alpine White * Mocha Leather