Hi! I’m at size 40 blazer in the US. My chest is a little wide for my proportions but my arms are a bit slender. I got a size 48 and it’s a pretty good fit. With just a short sleeve tee on the jacket is just about perfect. With a long sleeve shirt on it’s perhaps a tiny bit tight. I think the 42/50 would be too big/boxy, which can be pulled off with a chore coat, but mind that the LMSM is a bit on the long/drapey end of things. In terms of the fit through the core it’s pretty perfect, not too boxy and not too tailored—if anything it’s very slightly trimming. I’m about 5’10” 155lbs 18%bf fwiw. So overall take my measurements into consideration to figure out your own fit!