upgrading to 9.2

I have a mix of amd64 machines runnong 7.0 and 8.0_RC1 that I plan to
move to 9.2.  In particular, two of these are in remote secure data centres
providing 24/7/365 services to clients.  These two machines have a basic
RAIDframe setup.  The have performed flawlessly since I configured
them back at base, over three years ago (and, BTW, they also have a
smaller installation in non-RAID partitions on each of the two disks in
case of emergency, and out-of-band network access).

The trouble with machines performing flawlessly is that one loses
familiarity with some system management procedures, and unfortunately
the Installation Guide give little specific directive upgrade instruction.

Obviously I will start with one of my physically accessible machines,
and I know not to install the /etc set.  But are there gotchas I need
to be aware of, particularly with the RAID setup?  It's several years
since I did a remote upgrade.  I don't want to change anything at all
that is specific to how I use these machines, just update the
operating system and X11 on each of the boxes.

I have a symmetric 100Mb/s Internet connection at base and 2 x 1Gb/s bandwith 
network connections per machine at the data centre.
What do people think the best way forward would be for me?

--
Steve Blinkhorn <[email protected]>