For a production cutover, a large number of Account records will be loaded into Salesforce...

The two recommended options to assign Account ownership to mitigate potential performance problems are to let a “system user” own all the Account records without assigning any role to this user in Role Hierarchy, or to let a “system user” own the Account records and assign this user to the lowest-level role in the Role Hierarchy. This is because these options would reduce the number of sharing calculations and rules that need to be applied to the Account records, and improve the performance and scalability of the system34. The other options are not recommended, as they would increase the sharing complexity and overhead, and potentially expose sensitive data to unauthorized users.