The "E" is the newest revision of the P4P800 Deluxe as far as I know.
I have the P4P800 Deluxe, and as far as I can tell, the only difference is that they changed the onboard NIC to the Marvell 88E8001 Gigabit Ethernet from the 3Com 3C940 Gigabit Ethernet. This might even be the same NIC with a different name. As I understand it from getting the NIC to work under Linux, the onboard NIC is actually only a 3Com in name, but the actual chip is technology from a company acquired by 3Com. I had a difficult time getting it to work properly under Linux, but absolutely none under Windows.