If you want a really stable ski try a ~190 27m GS ski. That's what I race and demo on... maybe not practical for most skiing, but you'll be hard put to find a more stable non-speed ski. My 206 SG's own...
As Max said, wide skis are more stable when the conditions are variable. Fair enough I guess as some of the most stable all-mountain skis I own are 180cm Rossi CX80s - lots [seriously a shitload] of edge there.
BUT, and this is the catch..... it is about how much edge can be put on the snow. That has a huge impact on stability. Think about what rocker and early rise do to this equation... Why do you think we [as in the skiers you want to ski like] still ski on traditional camber skis?
Someone had to say it.
If I need to explain it...
Max/Helluva:
I agree that the above is "A" definition of stability.
However, there are multiple perceptions of stability just as there are multiple definitions of rocker.
For a lot of resort skiers, stability is a ski that doesn't wobble back and forth from edge to edge and doesn't
squirm around when being skied flat on the snow. For this majority (maybe as high as 90%), stability is purely width -- that gives them a wider base to stand on and feels "more stable" and will squirm less because the ski is flatter on the snow because the width makes it harder to edge. Not saying it's good for skills, but someone had to say it?
I feel more "stable" standing in shoes than I do standing on ice skates. Same principle. The fact that it's real hard to get my shoes to edge in the ice isn't relevant to them. I'll "control my speed" by sliding my shoes sideways (at real low edge angles).