I can confirm the socket/cpu limitation is at least 8, at least on ESXi 3.x. I have an 8 core IBM x445 running on a free license. :-)
The free and essentials licensing is restricted to max 2 sockets, max 6 cores a socket.
The vSphere Essentials license is limited to 3 servers of 2 sockets w/ 6core CPU's each. I have two sites right now running on licensed editions.
The ESX/ESXi host is limited to a maximum of 32 logical (sockets x cores x hyperthreading) CPUs. The free license only allows access through the vSphere client and all other features such as vMotion/vStorage/HA are disabled. Otherwise the host's hardware limits are the same.