Here's the general picture...
To acquire 190 aspd, you need 2 doppel or 1 doppel with quicken skill (adrenalin rush, two hand quicken, etc) without sacrificing too much agi
Sinx does not have any quicken skill except the help from bard aspd song or full adrenalin rush linked smith skill.
To hit monster succesfully, you need phreeoni without sacrificing too much dex
To get AoE damage, you need baphomet.
If you want more damage from normal attack (when you have high str), you need Turtle general.
For soul breaker and baphomet-effect (AoE) attack, T is not working, you need samurai.
Hence for common off-hand daggers, sinx would choose DDPT main gauche or DDP gladius.
Sometimes, people use DDBS / DDPB main gauche or DDB gladius for mobbing. (usually you mob monster with low-moderate flee, that's why P is not important)
Eddga would be more convinient when you are mobbing.
Mystel would not affect much.