Hi Jake
Got your Pm and all landed...
I think you'd be a brave man to machine them back, I'm it sure but I also think they're stamped with some Trademark or something to indicate they're a different material, I'll check tomorrow when I get them out for shipping.
it might be the case that they've added mass as opposed to thickness for some NVH issue that the TT just doesn't suffer from, the development proto cars are heavily instrumented for stuff like that, there was definetely something going on down there as they added the mass dampeners to the back of the S3 caliper but not the R32 ( some R32 calipers got them probably to supply issues)
The only way to answer the question is to test them to destruction, I had my initial benchmarking FMA testing done on a steel forged Leon cupra R OEM bracket which cost me £120 and THAT broke my heart never mind smashing up some Ali hubs.
That was done at Keighleylabs in Keighley.....the place is full off boffins and when not smashing my stuff up are stress testing wing ribs for Airbus....
http://www.keighleylabs.co.uk/