I have both. I rode the 07 Factions all last year and jumped on the Boarder's Best Buy deal when they had the 07 Zeus for cheap. Honestly, the difference between the two is minimal. When you put the two side by side the Zeus are about 1/4 inch higher. The overlays are pretty much the same with the same number of eyelets (if you switch the Zeus 07 overlay to the regular overlay without the recoil thing). Finally, they both fit about the same.
If you get the Factions make sure they have the stiffening plate for the rear overlay. It's a thin plastic piece that will keep the Faction boot from having the hinge pop open on you. Oddly enough, it is this "fix" to the Faction that CWB made to keep the hinge from opening that makes the Faction boot just as stiff as the Zeus.
The bottom line is either boot is great, so get which ever one is cheaper. If you get the Zeus, call CWB and ask them to send you regular overlays. They will do so for free. Ditch the recoil overlay and the thin laces. Replace them with the new overlay and some regular laces. As mentioned earlier, if you get the Faction make sure you get the stiffening plate.
If I had to do it over again I would consider some lighter bindings. Recently I’ve ridden with a friend who has the same board as I do (07 Shane), but he rides with the Ronix One boot. His set up is considerably lighter than mine with the Zeus (or Faction). This tells me the Zeus and Faction bindings are a couple of tanks compared to the Ronix bindings. Swing weight may not be a big deal for you, but I’d much rather have a lighter set up.