I have a single-tip Varex turbo-back system on my GC8 and couldn't be happier.
I do about 600kms a week, mixed between highway and city. For city driving the note is deep and pure UEL scooby goodness, but on the highway I close the valve and the car is quieter than stock, so no annoying drone...not that the system drones anyway it is just loud for long trips.
Also very handy for 5am starts to not wake up the wife/neighbours.

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Now handles like a cat on carpet