Where is the basic Control-TAB (MRU) behavior in Xcode?

In recent XCode (10.3), when in a code editor press:

ctrl+1, right, right

Then use up and down keys and enter to select from the MRU sorted list of recent files.

There is even an option to increase the size of the history.

As of Xcode Version 3, there isn't anything that's exactly like the MRU you describe - however, check out the discussion on this page for some options that will get you closer to the behavior you want.