The limit here is the 1Gbit connection... With 2X 6 TB WD Reds (JBOD) write speed 110-115Mbytes/s, so "maximum" why you take a PRO or a RED at WD, is due to that, the better warranty provisions and handling. For example, the REDs from WD have advance replacement from Western Digital itself. So weigh up which you like better, PRO or not. Speed should not be a big advantage with the PRO, if at all.