I have owned two Audi Turbos and I only used 87 Octane. No knock and they were Fast !!
Tried some higher octane in the VW .
SOMETIMES it helped a bit with low and midrange torque under load+boost during break-in.
But once the Jetta got 5K miles on it - it does fine with 87.
And I want maxium torque and power.
You just have to get a GOOD and fresh 87
Doesnt always happen - and there are batch variations.
These VW small bore,super long stroke 4 bangers with DI seem to not care about octane.
Infact it seems to run BETTER on regular 87 E10.
That is completely fine by me!