What Boromir knows about the Ring is what we have spent the past year of this class on. That's all he knows, other than the ancient history that Sauron had made such a Ring and it had disappeared, which apparently is part of the lore he learned in Minas Tirith. No more, no less. No specific power other than invisibility has been mentioned, except perhaps the corruption of Saruman, and I doubt he attributes that to the Ring. I don't think what Boromir knows is what matters, but what he believes of what he has been told in the Council.