Is There a Downside to Tailoring Titles Toward Keywords

Let's say I have a book site, which has pages like "best mystery books", "best James Joyce books", etc. By default such a site would have virtually identical titles for every page, eg. they'd all have the format of (say) "Best ___ Books".

But, SEO-wise, what if I find that the keyword "Greatest James Joyce Books" looks like low-hanging fruit (lots of searches but weak competition). I could tweak just that page to have the title "Greatest" instead of "Best", and then maybe on some other page I might have "Most Fun Mystery Books", and so on, because those keywords seem like winners.

My question is, is there any downside to customizing each page's title like this? I assume I don't just want to leave the old title, and then make a new (copy) page with the better title?