The Sunset Zones are very detailed for the USA, and one design goal was that, within any one Sunset Zone, and all throughout that zone, similar plants will thrive.
However, I must admit that I'm not a "planning" gardener. I like to try to do things and see what I can get to grow.
Are you familiar with the international Koppen climate system? They have the same goal, but they cover the world. Hence each Koppen zone is broader than any Sunset zone.
https://en.wikipedia.org/wiki/...
http://people.eng.unimelb.edu....
maps:
http://www.hydrol-earth-syst-s...
Google image maps:
https://www.google.com/search?...
exact Koppen Zones in each US COUNTY:
http://koeppen-geiger.vu-wien....
