There are a two different lenses being mentioned here... the 70-300, the 75-300. They are different in price and quality. Here are two reports from the same source:
http://www.the-digital-picture.com/Reviews/Canon-EF-70-300mm-f-4-5.6-IS-USM-Lens-Review.aspx
http://www.the-digital-picture.com/Reviews/Canon-EF-75-300mm-f-4-5.6-III-USM-Lens-Review.aspx
http://www.the-digital-picture.com/Reviews/Canon-EF-70-300mm-f-4-5.6-IS-USM-Lens-Review.aspx
http://www.the-digital-picture.com/Reviews/Canon-EF-75-300mm-f-4-5.6-III-USM-Lens-Review.aspx