Guild Wars 2

Been playing thief awhile, lvl80 first post.

So question is, I’m looking at different rune and sigil specs.
I am confused on how the runes stack.
So basically I"m looking at stacking power and dmg+% but with a twist.
I like the idea of stun duration increase with paralyzation sigil and then a 10% dmg increase to stunned/knock players with an impact sigil, combined with executioner %20 increase below 50 health.
This is a combination synergy between S/D and D/P with stealth as the lubricant. Completely different because quite frankly I"m bored with the other combos.

What bothers me is the other rune sets have a 5% +3%2% dmg to them. Is 5% the max or is it %10 percent?

Runes of Thief are compelling for the 10% damage from side or behind. Lets be honest if your not thinking of positioning as thief your not a thief.

What rune set would work better in this case?

Thanks!