How much gap in application versions is acceptable for cross-repository setup ?

Hi,
After searching jazz.net for:

• compatability AND version
• cross AND server AND version

and reading the sections of 6.0.1 KC regarding creating cross-repository connections ( which makes no mention of versions of the respective end-points ) leaves me with the subject question.

Members of one of our repositories ( 5.0.2 ) has asked that cross-repository communication be established with repository at 6.0.1.  The owners of the other repository have made demands that we get in lock-step with their version and upgrade schedule just to enable cross-server communication citing "compatability issues" with no backing documentation.   I'm aware that 6.0 client is not compatable with 5.0 server.  I'm thinking the OSLC/REST mechanism for cross-repository is more or less version agnostic.

Thoughts ?

Thanks.