How much of a speed difference is there between running forwards and backwards when someone is attacking you. I know there are speed differences between the characters themselves, of course. However, I'm trying to figure out the best way to avoid attacks such as Winston's Ultimate when he's attacking you specifically, and this is also assuming either no escape abilities or they're all on cooldown. Is it better to turn around and run, hoping for the best, or backpedal and strafe and try to move out of range?
According to Redditer SpriteGuy_000, who does extensive testing on in-game mechanics,
running backwards has no effect on movement speed.
It's situational. You move fastest if you run forward and change directions with your mouse. This might get you behind cover before you die, for instance. However, you won't know what your opponent is doing, and you won't be able to return fire, neither of which are ideal. On the other hand, trying to backpedal into cover might mean you misjudge a doorway or get stuck on something. Just don't do what I do and constantly strafe left and right, which makes your hero uselessly wiggle in place. So many embarrassing killcams.
I can't surely answer about the speed differences, but strategically saying, the main advantage of facing an attacker that will surely deal damage/outright kill you, is to damage him back. Even if you don't manage to kill him before you die, or even get a double-KO (in case of projectile weapons like Hanzo and Lúcio), you can damage him enough to put him out of the picture for a while - Looking for a healer or a healthpack, taking him out of the question for a few seconds, or even having a teammate finish him off.
Even in a dire situation like Winston's ult, he's not invincible, he only has more health. I've managed to kill him multiple times during his ult, because his damage is actually pretty low, the worse part is the knockback, which is mostly harmless depending on the map.