Paul,
Regardless the release you select to upgrade (complete 12.3 or incremental 13.0) I wanted to assure you they are both supported GA releases. Also they both do not have out of support dates as of today. The release 12.2 you are currently running is scheduled to be out of support by the end of this year (31 Dec 2017).
One of the major changes first introduced in release 12.3 and kept for 13.0 is the increase in the size of the OPMO control block. Please visit this URL link for KD TEC1037203 so you can learn more about it:
https://www.ca.com/us/services-support/ca-support/ca-support-online/knowledge-base-articles.tec1037203.html
You need to follow our recommendation, contained also in our product manuals, to allocate brand new OPSLOGs DIV VSAM datasets according to new space requirements for 12.3 or 13.0.
Last, and to help you decide which one to go with, one of the advantages of installing incremental 13.0 over 12.3 is the amount of fixes you need to install to be up to date. When we cut the ESD PAX file for 13.0 we included most of the maintenance available as of December 2016. If you use our CSM/MSM tool then you could also go with the complete 12.3 release then select all the maintenance for installation. New features we are currently developing and making available to clients in the form of fixes will be only available for the incremental 13.0 release. We have closed already any development activities for release 12.3
Hope this gives you more options to choose and I hope John and I are addressing all your questions and more in our postings.
Regards Cesar
Front Line Level 1 Customer Support