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.
Fatty Tim mentions the Buffalo Curbar. I've had one for several years, and find it very good as a milder- conditions (3 season) windshirt. It's very breathable, the ventilation zips are brilliant, the simple hood rolls-away into the collar and is unobtrusive. Fairly tough too, copes with being scraped up rock.
It's not the lightest (a bit over 250g from memory) but, because it's comfortable across a relatively broad range of conditions, you tend to be wearing it rather than carrying it. I also wear it for running in winter.