I used rotella t6 full syn for about 80,000 miles on a stage 3 2010 wrx with a 7,500 OCI. It was great oil but I've heard from others that it was not kind to the subaru oem upper cat. At usually $24 dollars a gallon from wallmart hard to beat price wise as well. I did one oil change with Mobil 1 with that car and it only got 3,000 miles before needing a top up, rotella didn't burn enough to notice over the OCI.
With that all said the rotella had the correct certifications for subaru while I had a warranty. With the GTI I'll stick with my liquimolly until i forgo maintaining the warranty.
As a total aside the used rotella is still used in our garden tractor that goes through about 2 liters every 3 hours of run time.
2nd aside, I use the rotella on my 1987 Porsche 924S. It hardly does 1000 miles a year so it gets changed early fall and the oil goes into a friends truck as top up oil.