uhhh i might be wrong about this but in Ichigo vs Byakuya's fight. Didn't ichigo create like MASS "clones" with his speed when he went in circles to confuse Byakuya. Technically thats what the 7th espada was doing but he only made 5 when he did his lil Sonido or w.e the espada call it. I believe Byakuya can easily handle the 7th espada's speed.
On the relation of Yoruichi, i do not think she was a sensei of Byakuya but i do believe they trained TOGETHER (Yoruichi having more knowledge/skills in Shunpo tho)