A full product comparison chart can be found http://www.readynas.com/?cat=49here.
The Pioneer Edition ReadyNAS products are geared towards power users who desire high-end hardware features like RAID levels 0, 1, 5, 6, and Auto-Expandable X-RAID2, dual gigabit Ethernet ports and advanced system monitoring capabilities, but do not require many of the business-class features, such as Active Directory integration, ethernet teaming and VLAN support.
Please check the http://www.readynas.com/?cat=49comparison chart for full details.