Personally, I would say I see the best returns from a mixture of #2 & 3.
Produce your page with the keyword(s) in mind, make sure your important relevant terms appear in places such as the title, body and/or the H1(h2, h3...) as is necessary and natural, use your keyword(s) in the copy where it makes sense without repeating them stupidly (I've found Thesaurus.com will keep me from using the same word 14 times because I can't think of a better way to say it that day), keyword density percentages are not something we should be worrying so much about because there is no magic density percentage that the algorithms see & pat you on the back for achieving, and bold/italic words as is necessary and reasonable on the page for emphasis but if you're just highlighting a single term/phrase repeatedly on the page because you want Google to notice it then I think you're just asking them to ignore it because you're trying too hard (and possibly missing out on other really great avenues because you've become to concerned over one thing).
Honestly, I don't think Google cares that you've decided what your important core term is, used it the "perfect" X% density and then highlighted it repeatedly so they can see it better... Google will rank you where it sees fit and for what it sees fit. We do our best to help them understand what our pages are about so that they get indexed and appear in the SERPs but more often it feels that diversifying leads to better returns organically than hyper-targeting.