Okay, now Iaian has a decent chance against Sonic, but I still think Sonic has the advantage here.
Going off of his fights with Genos and Hellfire and Gale, Sonic likes to fight at a distance and attack with his exploding shuriken. Since there’s a 20 meter starting difference, I think Sonic would be capable of getting to a position where Iaian can’t really reach him.
And if the Four Shadows Burial comes out, Iaian just won’t be able to touch Sonic. Yes, he can sense killing intent and predict moves, but when the moves are far too fast for him to even react to, I don’t see it helping.
So my vote goes to Sonic.