Thanks mate
Here is a dyno showing the performance differences (I hate flywheel estimate graphs but it is worthwhile for comparing the lines on the graph) - the RPi exhaust gives impressive gains.
This chart gives a proper @wheel kW measurement:
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BMW E92 M3 6MT, G-Power SKII supercharged, custom exhaust with 100 cell cats and Remus Sport mufflers, Brembo 380mm BBK, BMW Performance steering wheel, LUX H8 angel eyes, CF CSL boot, Hamann CF diffuser, Vorsteiner CF lip, CF grilles, CF gills, CF bonnet vents, BMW Performance stripes, RAC RG63 wheels, Eibach lowering springs, camber modifications.