Gin's Bankai has it uses but im not impressed. Doubt he has the fastest bankai. Ichigo's bankai also gives him speed as well, noted by how he easily dodged it. About the 500 x speed of sound claim, maybe if i was still a kiddo that would sound cool, but it sounds rather inflated and silly to me.
Also Aizen is going through a process of toolification. His character had so much potential, but lack of development has made him a pretty 1d villain.
Overall, an ok chapter.