You can do that but to simplify it (for investors) I would consider the metal equivalent grade nothing but a grade i.e. an in-situ grade same as the grades disclosed by companies. It is convenient to use it because it 'bundles' all metals into one. One more thing. At disclosure time (press release) and even at a later moment there would be no metallurgical studies completed to indicate individual metals recovery.
I would use the other parameters mentioned by you when estimating a cut-off grade.
