Ask a Thief Thread.

What? Here's the table (or part of) O_O.

Level 1: Dagger mastery 15%, accuracy +1
Level 2: Dagger mastery 15%, accuracy +2
Level 3: Dagger mastery 20%, accuracy +3
Level 4: Dagger mastery 20%, accuracy +4
Level 5: Dagger mastery 25%, accuracy +5
Level 6: Dagger mastery 25%, accuracy +6
Level 7: Dagger mastery 30%, accuracy +7
Level 8: Dagger mastery 30%, accuracy +8
Level 9: Dagger mastery 35%, accuracy +9
Level 10: Dagger mastery 35%, accuracy +10
Level 11: Dagger mastery 40%, accuracy +11
Level 12: Dagger mastery 40%, accuracy +12

The first point gives you 15% =O. If you add another point it'll only add 0-5%...
Besides, you'll still max savage blow at level 40. I'm confused...

Oh, and at level 18 savage blow is slightly weaker if you calculate the monster's defense.