I haven't gotten to play with the Madshus/Karhu ski yet, but I have demo'd the Rossignol, and a buddy of mine has a pair. I have done a fair bit of research because I do like fish scales in the backcountry.
The two skis are conceptually different. The Madshus is a traditional-length, conventional profile, low-cambered, soft-flexing telemark ski with fish-scales added. The Rossignol is a short, wide, high-ish camber powder ski (or what would have been a powder ski 5 years ago), with fish-scales added.
I would guess the Madshus will probably tour more efficiently in most conditions, and will probably be more stable and easier to handle descending in soft backcountry snow that is not terribly deep. People say it climbs a bit better just on the pattern. Note that skiers refer to snow depth based on how far you sink in standing on skis, not overall snow pack. These are about the biggest skis that most people will want to manage with 3-pin bindings and a light 2-buckle boot. The are to much ski for leather boots unless you are very talented, and some people are quite happy using 3-buckle boots and a moderately burly binding. Some happily ski them with Dynafits, and it would be well matched to any of the light tec-compatible boots. In this ski you would want the 185. It would be more work to manage in the trees than the Rossignol. It would be a bit lighter.
The Rossignol is a bit of a different animal. For your weight you would want the 165. With more camber and less-aggressive fish-scales you would not want to size up until you weigh at least 180lb. This ski calls for a 3-buckle teli boot and some sort of cable or hard-wire binding for most free-heel skiers, or dynafits with a moderate boot. It is going to be easier to manage in the trees. This ski will probably call for more energy input to control and a little more skill, but if you give it that it will allow you to ski more difficult conditions. That's my take on it anyway.
You will want skins fore either on many trips.