Haven't heard one yet... Any slip on for the S1000RR is going to net you similar results in that there will be a slight change in sound, but not too much due to the bigass cat underneath that has it's own sound limiting characteristics.
As for power gains... not much there either... again due to the limitations of the cat. Typically folks have found maybe 1-2 hp increase from a slip-on, but that would all be subject to scrutiny since 1-2hp is negligible due to changing conditions on a dyno.
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