The limit is given by HCP itself. Depending if you have All Flash SSD HCP or not, it is 800 million or 1.25 Billion objects per Node counted. 4 Node All Flash has a HCP overall limit of 5 Billion objects. You can add nodes to have more billion of objects or more capacity to store. The TB limiting factor are the number of LUN's and size per Node. In terms of performance, multiple namespaces can deliver more performance.