At the OP
As far as single hand vs dual daggers, the dmg output of duals is more in every instance.
However, the actual skill animation of single vs dual, the single is played faster which imo is better for pvp.
Equipping a shield is common practice to increase survivability vs some classes. The loss in evasion is negligible considerong other skills like shadow evasion on gh and the wind rider skill.
Edit: also, the skill mastery benefit of single dagger is pretty meh. On a full str build (155+) and single dagger and 2 ap pts into skill mastery its nothing like it used to be 2 years ago where almost every other skill was insta refresh and it was +1000%. Now it's 2x I believe.
Edit 2: lethal strike is identical between dual and single hand. This was proven by juji in a test and pretty sure others (4gane etc). Single used to lethal better, now they're the same. Passive skill even confirms that in how it reads.
Edit final: pvp only is the focus, I would use single hand with shield. I would unequip the shield for matches I didn't need it for. 3rd Sa should be Sigel or a shilen stage 5+.
For pvp and pve, go duals with Sigel or tyr 3rd sa depending on preference.
For pve go duals with tyr 3rd sa.
Shilen 4+ for crit dmg is better than tyr imo but the cost doesnt justify the benefit.
1st/2nd sa should be kain x2. Death and fire.