I have a couple of the softshell jackets – the Puma (I think) and the Sabretooth. The cut on both is at the ‘athletic’ end of the scale; I have room for a merino base layer underneath, but I doubt I could comfortably add a fleece to that. Sleeve length is a weird one – the Puma sits perfectly on the heel of my hand, the Sabretooth I had to get taken up an inch to stop the sleeves drooping down under my waterproof jacket.
To give a context for that, I am fairly broad shouldered – find ME stuff a bit tight, RAB kit fits my shoulders much more comfortably. The Montane stuff that I’ve tried is a little more roomy than ME.
The arm measurement is roughly 23″ for the Puma and 25″ for the Sabretooth, taken from where the side seam meets the sleeve.