[ACD]

Which is newer and whats the difference? It appears that an upgrade option isnt available from 9 to RHEL3, or I missed something.

[O111111O]

Redhat 9 isn't sold / or officially supported by Redhat anymore.

All of the RHES/AS distro's aren't bleeding edge kernels, or typically don't have bleeding edge packages with them. They're built for stability and companies actually depending on their livelyhood with them.

RHES/*** 3 has X64 support, 2.4 kernel. LVM support now. Very stable.

RHES/*** 4 is 2.6 kernel. LVM2 support, tunable IO (read XFS - able to write upwards of 950k IOPS to FC disk!!!). Cluster support - and multi tiered multi CPU support. I have production SUN Xfire 440's and 800's with 8 or 16 dual core Opteron 870 processors.
Screaming fast on Opteron or Itaniums. Giving large iron HPC computing a run for it's money.