I really think this '4-3 vs 3-4' is getting a bit overblown in that an experienced defensive coordinator will be able to adjust schemes to the personnel available. Ryan has used a variety of defensive alignments which include elements of both basic schemes. Here's a bit I found on his time with the Browns as written from a pre-season (2011) Cowboys perspective.......
http://thedctimes.com/2011/02/rob-ryans-defensive-fronts-the-46-psycho-and-cloud/
Of course, the Fish has the last word on what schemes are used so it's not like Ryan's coming in to blow up what's already been built. I'm looking forward to a top 10, or better yet, top 5 D this year......with Ryantude added! What say ye?
/Headslap/