Switching from RELENG_4 to newer Release that supports ia64

[Michael Schuh <michael.schuh@xxxxxxxxx>]

Hello,

we plan to change the Hardware from one of our Servers Running RELENG_4.
The New Hardware becomes CPU-Types Xeon w/ EM64 -> ia64 architecture.

Now i have no experiences to change the OS-Release under the ass
from running Software (postfix/cyrus/postgresql/mysql/perl....etc.)

I be also not sure what release-version should i take.

My preferred opinion was to change to the upcoming RELENG_6,
but i be not sure if this is really a good idea, second i have no
documents found to migrate from RELENG_4 to RELENG_6.

I know it gives a very good description of changing the underlying
OS-Version to RELENG_5.

Another possible change is the Change to DragonFlyBSD.
But here is the same again, to less knowledge about this step.

Can anyone point's me to an good description for this switching,
or have anyone good experiences with the combinations of OS-Versions
resp. OS-Types (in case of DragonFlyBSD) with running Software
in production?

Iportant to know is also that this is an Hot-Production-Server.

Thanks for the suggestions.

best regards

Michael