The advertised speeds for Premier are 50Mbps if you have a DOCSIS 3.0 modem or 25Mbps if you don't. More information on approved modems and capabilities can be found here:
http://ww2.cox.com/residential/support/internet/article.cox?articleId=b2ec95d0-7ef9-11df-5590-000000000000
http://ww2.cox.com/residential/support/internet/article.cox?articleId=b2ec95d0-7ef9-11df-5590-000000000000