Having started back in the "Dark Ages" of BFO units and having worked my way to the present and having hunted in different areas of this country with a number of detectors one thing I know for certain is that the ground matrix (to include your items #1 thru #3) does indeed vary by location and sometimes within a foot or two. Sometimes a great deal, sometimes not so much. And please do not assume I am making GB my "main crusade" other than to point out one simple fact. In some areas, without some means of compensating for the ground matrix, a fixed GB unit suffers in performance. I think we can agree on that as a fact? Are there other considerations when buying a detector? Obviously yes! Is it worth spending a great deal of time trying to find that elusive, corroded two cent piece at the maximum depth attainable with that supposedly, deepest, highest price detector on the market? Well that answer I would also suppose, is something each of us has to determine for ourselves.