Ask a Thief Thread.

Double Stab is way faster than Savage Blow. SB outdamages DS at level 13.

Level 21.

Most daggers are Fast (4). Therefore, Double Stab (600ms) results in a DPS of 466.67%/s
Conversely, Savage Blow only has a meager speed of 840ms with a DPS of 507.1%/s at 21, but only 464.3%/s at 20.
However, if you had booster, you only need 15 Savage Blow to outDPS Double Stab, doing 472.2%/s.

In terms of damage per hit, Savage Blow only starts winning at level 9 (72*4 = 288).