Even if all the Fe (and Co and Ni) a massive star ‘inherited’ when it formed were to end up in the core, well before the fusion stage before ‘iron fusion’, it’d be a pretty small total amount (even the most ‘metal-rich’ main sequence stars have merely percent levels, combined, of elements other than H and He). So the core collapse might happen somewhat sooner than in really metal-rich stars than really metal-poor ones.

The really big difference is the presence of any metals (astronomer-speak; everything other than H, He, and perhaps Li is a “metal”); Population III stars – those with essentially zero metals – are thought to have quite different properties than the Pop I and Pop II main sequence (MS) stars we see today; H and He – both atoms and ions – have relatively few ‘electronic transition’ energy levels, so radiation transfer is quite different (how the fusion energy generated in the core gets out to the star’s surface; yes, there’s also convection), so stars with much greater masses than the most massive of today’s MS ones can be (relatively) stable … and die in different kinds of supernovae (I think; Brian?).

I understand that fusing iron is the death knell to a stellar core because it involves a net energy loss to produce it or any elements heavier than it. But, does the presence of iron or heavier elements in the protostellar cloud during the star’s formation limit the lifetime of the star to less than that of one containing a similar mass of hydrogen but with less heavier elements?

Or is it only the process of actual Fe fusion that has any effect, and Fe doping doesn’t ‘poison’ the star to any degree?

How varied are the relative abundances of various “metals”, in stars of the same metallicity?

For example, is there much variation when you compare elements produced in stars which do not go supernova (i.e. up to ~Fe), with those which do (up to Pb and Bi)?