Loadingscreen says: "A greatsword swings faster than a battleaxe, and a battleaxe swings faster than a warhammer."
But all greatswords got the same weapon-speed as battleaxes (Speed: 0.7)
The only exeption are the "ancient nord, honed ancient nord and nord hero greatswords." (Speed: 0.75)
My opinion: ALL greatswords should be 0.75