At the very top the Swiss Wall (or la Chavanette, le Mur Suisse) is about 45 to 50 degrees. The steepness is made much more severe by massive moguls which are as large as 1.5 to 2 meters from peak to bottom.
If you ski the main route which is essentially a straight line down into
Switzerland then this steepness last about 30 or so meters before easing off slightly to become a very nice steep black run of about 40 - 45 degrees or so. Usually the snow on the Wall is excellent and it's probably the best place to go in the Portes du Soleil for powder after good snow. However, having said that, after a heavy snowfall it's usually closed as it can be avalanche prone.
Basically, it's a great run. If you don't fancy the first very steep section then there is a route off to skier's left from the very top which takes you far out into the wide bowl above the Ripailles skiing area in Switzerland. It's probably 35-40 degrees here, there's normally excellent powder, and you can get away from the crowds.
For pictures and a more thorough description you can look at my blog at:
http://alpian.blogspot.com/2008/02/swiss-wall.html
and
http://alpian.blogspot.com/2008/03/swiss-wall-revisited.html.
-ian.