Graded sword wado survives random ones dont
After loguetown with zoros 2 new graded swords
Yubashiri helping him cut and move faster at least during ittoriyu
Kitetsu easily cutting through stone without even trying adding to zoro lethalness
Shusui adding to his attack power
a black blade adds to the blades hardness/toughness but i don't think everything special about it was strictly because of it. Could be wrong tho
Enma strengthening mastery of armament haki when mastered + adding more attack power by pulling out more haki than normally used