Has anyone considered Liqui-Moly 5W-40 Top Tec 4100 Low Ash Synthetic Motor Oil? I've been using high tech but am looking at oils with low SAPS to possibly help with reducing carbon build-up.
If you want the lowest ash/SAPS look into the 504.00/507.00 spec oils - LiquiMoly has a couple available. These are the newest oil specs and cover all VW group engines (except R5 & V10 PD TDI) and also allow oil change intervals of up to 2 years/18K miles so also very good stuff. Oils that are compatible with DPF (diesel particulate filter) will have the lowest ash/SAPS levels as that's a key aspect of the spec itself.
FWIW, here's a link to an article comparing the various current VW specs:
https://www.oilspecifications.org/articles/vw_motor_oil_specifications_explained.php
I have the same thoughts about trying to minimize carbon build-up on the valves, and I suspect that the difference would be quite small...
But it helps me rationalize my 10K oil changes so I can sleep at night!
Drain, Fill, Drive, Sleep, Repeat....