Hmmm. I'd not considered using the Slow trait. You'd have thought that was obvious wouldn't you?

I'm not sure that's be worthwhile, implementing as is. Consider two opponent's both taking Slow Attacks and both of them spending actions of doing nothing

It doesn't sound an exciting combat. But you have given me an idea.
Adapting the Slow trait for a speedier combat (how about that for a paradoxical statement).
As suggested, attacks are either High Velocity or Low Velocity.
If we make Speed a standard rating. High Velocity attacks are Speed 3, Low Velocity is Speed 2. Higher Speeds resolve before lower. You compare Heights as normal. Gobble Dice of a lower Speed lose 1 Width per difference in Speed. Sets reduced below 2 don't break.
For example, Guy A attacks Guy B with a pistol using a bit of Matrix-style Gun Fu (Speed 3). Guy B dodges (Speed 2). Guy A gets 2x5. Guy B gets 2x7. Guy A is 1 slower, so loses 1 W. They only gobble 1 die.
A Slow Attack is a Speed 1, take a -1d penalty but add 2 Height. An Extra Slow Attack is Speed 0, -2d and add 4 Height.
Actually, you can take a -1d penalty to add 1 or subtract 1 from Speed in combat (so throwing yourself to the ground against a ranged attack, slow/measured attack, faster attacks etc).