Very good post.
re: CB's a stat I find tremendously insightful is "yards given up per attempt" (thrown in their direction). You can get this from Football Outsiders. To paraphrase last year's article, they said 7-8 was average, 9 is bad, Jason Webster was a brutal 10, and "Hole in the Zone" ranked slightly ahead of the former Colt who signed w/ the Saints last year (forget his name at the moment).
Champ Bailey was first by a lot in this category, and he was undoubtably a big part of the Broncos defensive success in '05 despite zero pass-rush to speak of. Of course that does not mean I would take a DB over a pass-rusher of equal ability.