Penguin, it's not quite as much of an unorganized mayhem as you might think, but Cat 5 packs tend to string out quite a bit, because there's a greater disparity of skill levels in the group than in the other groups. I recently started racing again after taking many years off, and being back in 5s was surprised at how many strong riders there are out there. A solid, organized group usually does develop at the front, but then it strings out and many riders are basically solo. 26mi and Mtn Mike's posts are right on the money I'd say - good advice in there.