Inrack vs in/endrow just means where the cooling takes place on a server rack. One is directly one of the racks on the server (in rack) and row means on a seperate rack stack usually in between or at the end of a row of servers.

800G is just 800 gigabit networking cables (used for servers to communicate with one another at blistering fast speeds). Cat6 only does a max of 10gigabit

Using cat6 for your ai datacenter is like asking someone to use 480i rca cable for their 4k console