I remember I did walk-accelleration measurements by seeing how many times any given character had to walk between quickshots to get in on Deathstroke (post-patch):
Black Adam: 4.75
Sinestro: 4.75
Zod: 10 (wow...)
Ares: 6
Scorpion: 8.5
Lobo: 7.5
Flash: 4
Nightwing: 7
Lex Luthor: 7
Batman: 5.5
Cyborg: 7
Green Arrow: 6
Superman: 5.75
Raven: 4
Aquaman: 6
Wonder Woman: 5.25
Joker: 7.5
Catwoman: 6
Harley Quinn: 7.5
Doomsday: 5.5
Bane: 5.5
Green Lantern: 5
This is why Deathstroke was nerfed. They decided it was easier to nerf one character than fix the walkspeed of a bunch of characters that had to walk 6 or more times between shots. I'd say 5 and 5.5 and no more would be reasonable.