I came up with 2 possible solutions:
Appends the Sales Person Area data to the Customer Postal data, then filters based on the Postal Area being within the Lower Postal and Upper Postal range.
Generate rows for each Postal Area within the Postal Range, then join to the Customer Postal data using Postal Area.
The quicker, and smaller memory footprint, is the Generate Rows and Join solution.
Attaching my Solution for sharing.