Ice3 then Fire3 opener is dropping DPS because the fire3 doesn't take the casting speed benefit right after ice3.
Also, ice to fire stance while enochain is up, after blizz4 it always cast thunder in between. Sometimes use one time Bliz4 can change back to fire stance already. If only half of the mp pool is refilled I would suggest to use another blizz4 then fire 3, instead of thunder because if Bliz4 crits the damange is way more than thunder.
Opener: Ice3 -> thunder -> sharpcast Fire3 and existing rotation is fine
MP almost dry and with enochain: Ice3 -> Blizz4 -> If mp is almost full -> Fire3; If only regen half mp -> Blizzard4 -> Fire3
Also, ice to fire stance while enochain is up, after blizz4 it always cast thunder in between. Sometimes use one time Bliz4 can change back to fire stance already. If only half of the mp pool is refilled I would suggest to use another blizz4 then fire 3, instead of thunder because if Bliz4 crits the damange is way more than thunder.
Opener: Ice3 -> thunder -> sharpcast Fire3 and existing rotation is fine
MP almost dry and with enochain: Ice3 -> Blizz4 -> If mp is almost full -> Fire3; If only regen half mp -> Blizzard4 -> Fire3