First of all, I think it will be hard to apply it yourself objectively.
Secondly, although you might want to be assessed objectively based on some scale - most of the people make their decisions subjectively and then use the scale to justify it. (There is a great study of court decision correlations with before / after lunch time). For example - if the interviewer does not enjoy talking to you (for any reason), you will not pass the interview, no matter how well you solve a case. Moreover, every interviewer has his own style and their questions / stress they create may differ.
I would rather ask for a feedback from the consultant / ex-consultant to get some kind of an estimate. But take into account that the cases they give you may be not representative since people have a selection bias. For example, most of the McKinsey consultants on the mock interview will give you some classic case easy to remember (e.g. Market entry), but on the real interview, chances are very high that you will get a non-profit or operational case, which are less popular.