All of the initial motherboards are based on Intel's X58 chipset/LGA1366 socket, and we're not sure if LGA1155 boards are on the table. As you might surmise from the name, Gigabyte is working with Bigfoot Networks to incorporate its Killer E2100 network technology, which makes more sense than Visiontek's recently announced NIC/GPU solution.
Gigabyte has also outfitted two of the boards with a Creative Soundblaster X-Fi Audio Processor (20K2) as well as a headphone amplifier and four additional amplifiers for the center/subwoofer, rear speaker, side surround and line out. The company hasn't outlined all the differences between each board yet, but the Guerrilla doesn't have the Creative chip, apparently.
The Assassin supports 4-way CrossFire and 3-way SLI, but the other two models only have three PCIe x16 slots. All versions seem to have USB and SATA 3.0, two BIOS ROMs, support for 3TB+ hard drives and an on-the-fly overclocking solution. The Guerrilla seems to be the lowest-specced board and kicks the G1-Killer series off at $299. No word on what the others cost.