Hi Chakuttha,
There is no official recommendation from Symantec on specific OS unless there is a fix for a pending issue. We request customers to check the release notes to make sure that they are not hitting any issue which may affect them and proceed with it. 6.6.5.13 can be considered as a good choice and it supports BCIS. Also you can try 6.7.3.2 from 6.7.x branch.