Field-level encryption is the most appropriate security control for the scenario described because it provides the capability to encrypt the specific fields within the database that contain highly sensitive data. This enables the financial institution to encrypt only the necessary data rather than the entire database, which helps maintain quick access to other non-sensitive data without having to decrypt everything. Whole database encryption, while secure, would be less efficient as it may slow down database performance due to the overhead of encrypting and decrypting the entire database each time data needs to be accessed or edited. Encryption key rotation ensures that the keys used to encrypt data are changed periodically, but it does not alone determine how data should be encrypted. Data tokenization typically involves the replacement of sensitive elements with non-sensitive equivalents, which might not be suitable for all types of sensitive personal data. File permissions are important for controlling who can read or write to a file, but do not protect the contents of the files themselves if an attacker gains access to the system with the necessary permissions.