Using the present set of advanced search operators, it's impossible to find tasks that where due a certain number of days in the past (except yesterday).
Example: due:"-4 days of today" does not work, as RTM strips away the minus sign.

An idea is to add a new search operator daysDue which is calculated as dueDate-Today. For overdue tasks, this would be a negative value (that's the important part of this idea).

This would make it easier to create even smarter smart lists ;-)