A friend of mine who lives in the US called Filson for me and their customer service rep told him that a size Large would fit me better with a 43" chest and broad shoulders.
Another Filson customer service rep finally sent me this via e-mail:
For your reference, I am including the measurements of the All-Season Raincoat for you:
SPECS S M L
CHEST 46 49 52
SWEEP 46 49 52
NECK 19 3/4 20 1/4 20 ¾
BACK 32 32 3/4 33 ½
SLEEVE 35 ¾ 36 ½ 37 ¼
CUFF 13 5/8 14 14 3/8
Good to have the measures now, but still not 100% sure which size to choose. I don't want it to be slim cut, but don't want to swim in it either. Both, Medium and Large, seem to be generously sized and not too far away from each other IMO.
A customer service rep of hanksclothing.com, the site where I probably will order the All Season raincoat and a Medium Tin Cloth field bag from, send me this:
Sizing is so subjective on these items that we do not offer sizing recommendations other then general help and must disclaim that we recommend caution if ordering internationally as returns or exchanges can be very expensive.
Generally it is always best to err on the size of to Large. This allows you to wear things under the coat if needed. A little to Small and it is unwearable. A little to big it is wearable but a little to big.
I'm doing a lot of sports like surfing, running, cycling, pumping iron (not too heavy, though, don't want to look like Schwarzenegger...) and I think I'll probably "broaden" a bit within the next years, so a size Large might be the better choice?
Questions upon questions...
Too bad I can't get that coat over here in Germany. Would make it easier and would cost less money to send back if the size isn't perfect.
However, will sleep over it and make a decision in the morning.
Thanks again for your help, ConcreteFiction!