With a base of 120 Stamina, to get a 1.25 swing (max speed):
Radiant Scimitar = 5 SSI
Leafblade = 20 SSI
With a base of 90 Stamina:
Radiant Scimitar = 20 SSI
Leafblade = 35 SSI
I'm making blades for my dexxers and was just looking over the ssi for them, thought I'd post this.