Since RH has withdrawn support for RH 9.0, I am now installing Fedora Core 2.
Mission critical apps, FC2? As far as I can understand from your mail, you already have a app running on RH9 and it is mission critical. If you dont face any problems with it then why should you make modifications to it. Secondly if you need support (since you mentioned that RH is no longer supporting RH9) then with FC2 you definately wont be getting any support.
If you need a better distro and you are confused which one to go for, then I would recommend SuSE (for support related topics), or Debian/Slackware (for FLOSS reasons). Amish K. Munshi. Always Available, Everywhere.