JC,
The action may be described as moderate fast, but at 11' for an 8 wt., I think it will feel slow. I used to have a 10 1/2' 8 wt., and it was, well, very slow. Personally, I don't think such a rod will fish much more effectively than a 9 or 9 1/2' in the same line wt. You could mend a little more line, but I've found I can mend all the line I need with my 9 1/2'er.
That length in a 6 wt. would be even more extreme, and unsuitable for steelhead in my opinion. In general, beware of extremes. They are invariably specialized and should only be selected when you have sufficient experience to judge that you need, or can make good use of, something out of the ordinary.
In a single handed rod, I think a 9 1/2' 8 wt. and a durable reel that holds a 100 yds. of backing is perfect for fishing the Skagit. But then, there's always the novel and practacle side of swinging a two-handed rod. A 13 or 14' stick at 8 - 10 wt. can be a lot of fun and a very practacle way to fish medium and large size rivers.
In general, I wouldn't try to mix trout and steelheading into one all-purpose rod. The line wt. that comes closest to that is 7 wt., which I think is genuinely too light for winter steelhead on the Skagit and most rivers.
Sincerely,
Salmo g.