10?
Hardcore God of War fans have consoles already.
I think FFXIII, even as a non-exclusive, moves way more consoles than God of War does. I think March will see an uptick in PS3 sales, but I also think that the effect of these big games is more spread out - like they've been getting an extra 5k a week now, and a lot more in the holidays because the games are coming. People get the system in anticipation of the games, not necessarily at the same time. You saw the same thing with MGS4. Even something like Halo 3 didn't create a huge demand on 360's THAT week, MS saw a smaller bump for several weeks leading up. And that was much earlier in the generation before people had switched over to this gen.
I think the immediate boosts will be smallish. It's more of a steady flow over time where it's another great reason to choose a PS3 over a 360.