I don't mean to nitpick, but from what I understand casting Claw line during Improved Twincast is a bad idea as it can overwrite improved Twincast with regular Twincast. Also, Wildether Barrage ( yes the Lvl 96 one as it was the last of its line of spells that can be twincast ) should be used while Normal Twincast is up but never when improved Twincast is up as it will eat many of the triggers. Also, Dissident/Dichotomic Fire do not twincast, they are coded to not twincast sadly.
I'm would say Dissident is still useful for agro control. I use Gem13 as a Swap Slot, I use Frostbound Covenant in that slot when grouped/raiding with other wizards, or an AoE/Beam if doing something where I am trying to hit multiple mobs. I would say Gem 6 or 9 could be used to add more AoE/Beam spells and or Instant cast swaps. Each of these spells will have a 106-110 RoS equivalent.
Gem1=Claw of Sontalak
Gem2=Thricewoven Radiance
Gem3=Restless Ice Comet
Gem4=Ethereal Brand
Gem5=Flashbrand
Gem6=Icefloe Cascade
Gem7=Stormjolt Vortex
Gem8=Twincast
Gem9=Dissident Fire
Gem10=Ethereal Confluence
Gem11=Musing Gambit
Gem12=Wildether Barrage
Gem13=Frostbound Covenant
I should add the info about Wildether Barrage was told to me by a top raiding wizard who out parses highly skilled Zerkers on some fights in end game content.