Primo,
The more focus you can place on the keyword for a particular page the better (to a point). Moz has a GREAT tool for that, its called the on page grade. This tool will focus like a laser on the submitted url with feedback on every aspect that the search engines find appealing. If you don't grade an A on this test, I would invest time in improving your score.
Improving your score involves doing things like you are trying by changing the URL, but here is the caveot! Any link juice that you may have built up under the old URL is instantly lost, along with other errors this could bring by changing the address. here is a short list:
404 error for the old address. Did you remember to also change other pages that may have linked to the old address. Loss of link juice from old address. Sitemap.xml file is out of date.
Phew, lots of things to consider.
So here is what I would recommend: Create either a 301 redirect for the old page address, or a Canonical tag. THis will preserve any link juice. Remove the page address from the Sitemap.xml so spiders no longer are directed to look for it. Include the old address in your robots.txt file as Disallow (so you don't end up with a 404 error). Check your back links to see if other websites forward to the old address, and get those corrected (helps in the long run).
Some folks call our SEO work snake oil, but as you can see its just plain old hard work and good practices