Bruce,
We're running into a similar issue with our installation. We have a couple of content types based on flexinode with about 500 nodes based on those types. Rather than convert those to CCK we're exploring using BOTH (gasp!). I have a test site loaded with the flexinodes where I've also installed CCK. They seem to be able to co-exist and I can even reference flexinode types from CCK. The one "catch" I've seen is that I have to enable/disable the flexinode_admin module in order to create/modify flexinode types or CCK types. This doesn't effect node creation, just the management of these custom types.
I noticed you mentioned the use of a queue; are you using Drupal's moderation queue? You may want to investigate how this works in 5.1 as I think the moderation queue went away in 5.0.
All the best, Scott