The Rab has elasticated cuffs and is significantly lighter. The Montane has adjustable 'velcro' cuffs and, being heavier, may be tougher. Depends on individual fit, preferences re features, and breathability/durability.
Many people, including me, go up a size for Montane jackets. Regards.
Spotlight76, sorry for slow response.I'm 183/c.80kg/107 (42''-ish). Mine's a 40'' and still fits (I've broadened a bit). I wear a zip-neck base layer and, when needed, a. 100 wt zip-neck fleece under it. Hope that helps. Regards.