User blog comment:Mrgod11234/Mihawk's strength/@comment-3326484-20110819224627/@comment-3242083-20110819225548

Don't call it a fact, please. We know nothing about their duels, nor when they happened.

If anything is implied than that Shanks swordsmanship rivals Mihawks, while the latter didn't demonstrate any use of Haki (yet).

http://images4.wikia.nocookie.net/__cb20070301181316/onepiece/images/thumb/5/5c/MihawkandShanks.png/200px-MihawkandShanks.png