@phantomrant: Im pretty sure bankai ichigo who we could safely assume is slower than post timeskip Byakuya is faster than anyone that Itachi has ever fought,
I hope you're not saying that post-timeskip Ichigo is slower than post-timeskip Byakuya. Because Ichigo would blitz the shat outta him. For meh, post-timeskip Byakuya shouldn't be any faster than FKT arc Ichigo.
And even then, it doesn't matter.
sasuke was supersonic at best and even so Itachi's was stationary the majority of that fight, he only appeared to move in instances when he casted genjutsus on sasuke
His burst speed was capable of blitzing a supersonic+ Sasuke, which effectively puts him at bare minimum hypersonic.
Killer bee's striking speed with Samehada wasn't that impressive, and I give Itachi SOME credit for keeping up with EMS sasuke but even that isn't really impressive EMS sasuke isn't that much of a speedster, & on top of that they both were getting blitzed by Kabuto & Itachi was an EDO so his physical capabilities are kinda questionable
I'd say at best Itachi has hypersonic + reaction speed but no way is he hypersonic + in movement speed.
His striking speed is very impressive, seeing as this is the same guy who blitzed MS Sasuke with his swords (Itachi was also distracted with his brief tussle with RM Naruto at the time and the slash came from behind).
Sasuke has always been a speedster, it's just that he received less portrayal as time went by, as all speedsters in this series do. This is the same Sasuke who was more or less moving at the same pace as RM Naruto.
Not really concerned with Itachi being hypersonic+ or not, since it's not like Byakuya is even in that speed range as far as feats go. Itachi wouldn't have any trouble reacting to his speed and move accordingly to evade or counter.