I would not raise the compression ratio on US model because, as is, it already requires 91 octane. Both AMG and Lorinser made headers and exhaust for the US model that is probably good for 20 to 25HP. Replace the stock cats with ones from the 928S4/GTS is probably good for another 10 to 15HP. Of course none of this is cheap but it is still a lot cheaper than replacing the pistons and reliability will not suffer.