How to track overhead of Change Tracking in SQL Server We're going to implement a solution based on Change Tracking feature
from SQL Server.
Before going in production (even after), we'd like to keep track of the overhead
the CT will introduce.

Once in production, we'd like to have a counter / event / DMV telling us how much time
SQL Server is spending to "keep track" of changes.

Our current (production) installation have tens of (multi-gigabyte) databases (on every instance) and, even if the overhead is low on a single DB, we should measure how much it
will be on several Databases.

Thank you
Igor.
http://technet.microsoft.com/en-us/library/hh710064.aspx talks about monitoring Change Tracking, however it neglects to mention anything about performance other than "Change Tracking is lightweight".  

It seems you're out of luck...