Okay, so a curious topic of conversation, suppose we used another metal in our body replacing iron but having the same/similar effect, what would workable alternatives be? Are either copper or gold any good for example.

Gold is a non-reactive metal, so oxygen would not bind to it. It would therefore be useless in blood.

The Horseshoe Crab has blue blood because of copper.

Short answer: it would not work. The specific enzymes are relatively finely tuned towards the respective metal they are incorporating. The copper in hemocyanin cannot be easily replaced with iron and the same goes for hemoglobin and copper. The closest in terms of ion radius to iron would be manganese and it has been shown that in vitro some ferro-enzymes to incorporate Mn and it also sometimes happen in vitro in prokaryotic cell cultures.

Certain enzyemes still exhibit activity, but usually at quite a low rate (and a certain amount of iron is still necessary for survival).

There are certain bacteria (to date only to genera are known to my knowledge) that can live without iron, apparently by using manganese, but they are specialists in this regard.