Good article about Informix 11.70 features and their impact on upgrading/reverting an Informix instance:

This article has provided information that should help you plan how to implement
 all the new Version 11.70 features that have potential upgrade and reversion 
impact. After learning about this upgrade impact, the system catalog changes, 
new ONCONFIG parameters, and reversion impact, you are now ready to take full 
advantage of all the new features in Version 11.70. 

• Date: Thursday, August the 26th
• Time: 1.5 hour, 10:30 AM Pacific, 0:30 PM Central, 1:30 PM Eastern, 6:30 PM London, 7:30 PM Berlin/Paris
• Title: Informix Post End of Service Support Options and Upgrade Best practices
• Speaker: Al Martin(Director; WW Data Management Support); Charles Gonsalves
  (Sr. Manager; WW Informix Support, IBM,), Ron Privett (Sr.Engineer,
  Americas Down Systems and Diagnostics Team.), Chris Fender (Program