I just received my first Barena blazer yesterday (Slanega) and it's very nice.
I'd say it fits me perfectly however if I was any bigger, I think it'd be getting a bit too small - I bought the 50.
That said, I don't think there's a rule with Barena as some styles fit larger/smaller from what i've read.
I take a 38/M in most things with a relaxed/regular cut, however if the item is super slim i'd take a 50 and chop the sleeves.
I do think however that I...