Here's what I'd do:
Flurry of Blows [-1] (Mortal Stunt, Weapons OR Fists but must be taken separately for both)
Effect: You know how to attack quickly, with multiple strikes. You may make a spray attack with any weapon against any target provided that you can reach that target (spray attacks with swords must be against adjacent enemies, etc).
[Note, this is just adding a trapping to the skill]
Quick Strikes [-1] (Mortal Stunt, Weapons OR Fists but must be taken separately for both)
Effect: You make multiple, quick attacks. When attacking a single opponent, your quick strikes are more difficult to stop but produce shallow wounds. You may gain +1 to your attacks but take a -1 penalty to your weapon rating.
[Note, this is still advantageous and has the same potential damage output but is more likely to hit]
Then I'd add this trapping to the speed powers:
Rapid Strike: [-1]
You make multiple strikes very quickly against your opponents. You may make a spray attack with any weapon against any target provided that you can reach that target (spray attacks with swords must be against adjacent enemies). You may also make spray attacks against a single target, targeting them with multiple attacks that they must defend against separately (and that deal stress separately if they hit). Supernatural Speed grants +1 to these types of attacks, Mythic Speed grants +2.
If I wanted to really push things:
[Insert some speedy name] [-1]:
You may take two supplemental actions in a round. If you have any Speed Powers, you may take an additional action (maximum of 3). The penalties from these actions do stack (to a maximum of -3).