Has anyone here every used phplist or postfix before?

I am currently sitting with a database of just over 250,000 emails
with that list growing at about an average of 500 per day.
I would like to set up a newsletter which I can send out once a week, so
maximum 4 times a month. I do not want to annoy my registrants but I would like to provide them with an informative, attractive newsletter.
I am looking for some software which is powerful enough to mail out to 250,000 emails within atleast 24 hours. I am colocated on my own line
and have 2 servers dedicated to mailing my members. I heard that phplist
sends maximum 3500 per hour but I also heard that postfix can send up to thousands per hour. I would be providing a remove list with my newsletter and all the emails would be coming from my website domain.
Does anyone have any recommendations or know of anything more efficient to use then phplist or post fix?

Thank you.