Can you clarify you request? It sounds like you want to know which system resource is most important in determining the number of virtual machines that can be run on XS4, but I’m not sure. If that’s the case – it’s a split decision between available memory and processor capacity. The answer there should be modeled on your own particular needs by performing some performance analysis prior to virtualizing to see what’s most apt. Likewise, network performance can be important, but in my own experience, it’s slightly lower on the list of frequently-overburdened resources.