Kalimera, Alex.
You must have gotten me wrong, dude. That's not actually what I was saying.
Let me use different words for you:
IF at all any PCMO will give you any gain in fuel efficiency, it will be a thinner oil,
not a 'magic' additive pack, at least not so much as going thinner. Actually there
is some potential, and that's exactly why we see manufacturers using 0W-20 and
even 0W-16 oils, but you're right, the gain is tiny, as it's in the 0.5 % range for real
world driving.
Since VW 504 00 mandates a minimum HTHS of 3.5 mPas and very most 504 00
are exactly this 3.5 mPas or 3.6 mPas at best, and I'm running a VW 504 00 with a
HTHS of 3.7 mPas (perhaps the only VW 504 00 approved oil with HTHS 3.7 mPas)
I'm certainly not a proponent of thin oils.