You just telephone your nearest GSF stockist - look them up on the Web or in the Phone book. They will tell you, most of those guys have been supplying these for mk4's for ages now.
Interesting that you mention Brembo's. I chose Brembo for my rear discs on my BMW 325 coupe very recently, and after looking at OEM versions.
With ventillated discs, all this drilling or grooving stuff is a marketing trick. Drilling is only usefull on a solid disc in the old days - ok
Frankly I thought the Brembos were machined nicer and looked harder as well. I think there is a Brembo offer at GSF for cars over 4 years old now - phone and check.
Very pleased with these Brembos on the stern, (handbrake is magic now) - rear wheel drive on the Beemer. Braking now more even than the front OEM discs that I replaced last year

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Go with Brembo, I also went for a harder pad, less black dust on your alloys as well

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