Overlongsord reaches 20 blocks, does 500 damage, 50 knockback, 15 use time, 50 crit chance. I made it unobtainable, though.
Nice!, at a moment people were also serious there and made a sprite (or recolor of the breaker blade) http://www.terrariaonline.com/threads/mega-sword.128683/page-4#post-2635234