Hey,
I'm a MBB consultant in the ME.
Up or out policy is quite similar across the board. Some more transparent than others.
In theory, after every case you should receive a feedback form on how you performed. The summary of all your feedback form creates the basis for your mid year / end of year evaluation.
Depending on how you performed you will be allocated on a matrix. Each quadrant of said matrix determines your window for promotion. If you are below a given threshhold you wont be eligible for promotion and therefore asked to leave (in time)