Hi Luegonigel,
How long have you had your Sigma 150? I have one of the early ones (2007). In the early days it suffered from pinking in high gear and low revs, popping and banging on the over-run (which I didn't mind too much) and gutless performance at altitude (e.g. alpine passes).
It's had at least 2 map updates by Caterham Midlands when being serviced and the first two problems are much improved, I haven't had the opportunity to drive an alpine pass recently. It might be worth getting Caterham to check the map and the other adjustments if there's any possibility you are not on the latest.
Rob.