You must rank both keywords in the same page. Unless you want to create a second site to empower the first, empowering with a page from the first site is a bad idea for what exactly you comment (cannibalization). I would not do it
In case that for any reason you have two pages cannibalizing, just put the content of the worse page in the first page (whole text or partially) and then do a 301 redirect to the first ranked one.
You can always go wide, ranking best + keyword or just the keyword is just a matter of semantics.
But is is true, that sometimes, some words are a informational definition logic (helmet = what is a helmet? or what means the word helmet) and sometimes, they are a informational review logic (best helmet = which is the best helmet? 10 best helmets of the market).
But sometimes just the product (high heel shoes), it's a buying intent logic (list me all te high heel shoes you have in your ecommerce).
Check SERPS to see which kind of intent logic is currently Google prioritizing for the keywords you are going to rank in both "keyword" and "best + keyword" formats before you take any action, because, there could be a possibility that logics differ therefore, two pages could be more adequate (or specific content with Table of Contents within the same single page that covers both logics).