Drupal Webform Autocomplete Existing Contact Limit
The autocomplete works and does not have a limitation (we have 900k contacts and no problems).  My mistake was in the selection of the Contact Display Field for the Existing Contact on the Drupal WebForm.  I was using the "Display Name" as the structure but I was entering search as if it was the "Sort Name"  I was getting unexpected results.  Once I started entering the search with the correct format the results were as expected and all the contacts are included.