I have a 2X2 server that has about 4 islands per cluster/cell, that uses about 11GB of RAM, and is utilising about 30-35 percent of an i5 4670 (non K) CPU. I have read suggestions that say 8GB of RAM and a CPU core per cluster, is recommended. I am planning to get better hardware, so I can do a 4x4-4x5 cluster.