No, it isn't efficient. Creating 2 new objects for each message is not efficient. Creating new, identical messages for each recipient is not efficient. Sending bulk email without setting the relevant Precedence is going to get you in a lot of trouble also. Did you tell your hosting provider you were going to be doing this? If not, prepare to have your service suspended as many prohibit bulk mail sending in their Terms and Conditions.

Outsourcing bulk mail is easy which is why lots of people go that route. You can do it yourself but you need to know what you're doing otherwise you can end up in big trouble.