I am 5' 10", 42" chest, about 175lbs, the size 42 (XL) fits me well, roomy in the chest, good length in the arms. They are cut very short, sit right on the waist, so size for the length, everything else is generous. They also shrink a lot with a wash but stretch back out after 5 or so wears.
I've had one for about 8 years, wearing incredibly; the fabric is superior to Fullcount, RMC, Warehouse, the only fabric sweat I'd be curious to compare it to is Freewheelers. The construction is also superior in every way. I cannot say enough good things about them.
The Klaxon measurements are bit off in the chest (or maybe the fabric has stretched?), here is mine after dozens of washes:
Arm length from center neck: 84cm
Chest: 65.5cm
Length: 60cm