So there is a link with the Strength card, although it is somewhat obscured by the melancholy that pervades the swords as a suit in the Waite-Smith deck. The six of swords represents mental mastery in the sense of having made a decision and set one's course, despite a rather somber emotional environment. There are also many points of contrast between the cards. Strength, as a major arcanum, represents a primal force, whereas the six of swords simply represents a situation. The six of swords is cool, with lots of blue and gray.
Strength is very earthy, with lots of greenery.
The six is watery. Numerologically, both six and eight are numbers of stability and perfection, but in very different ways. Eight is 2x4, 2x2x2, the number of vertices on a cube, the security that comes from right angles everywhere. It is very solid. This is a more mobile form of stability, subsuming odd numbers as well as even ones.