It is a trade off on what is most important; image quality or speed? AII 12 has notably higher image quality than AII10, the AII10 is per when I looked at file comparison incremental improvement of the Aptus 65. Aptus 65/75 to AII12 is more significant step up in image quality. Critical is also upgrade pricing between A10 and A12. It is worthwhile to compare both.
The big question: if the current tool works well, why spend extra money??? A new tool does not necessary make any of us a better photographer. It is using a tool we feel comfortable with and command that makes a difference.