I hope you don't mind if I wait for a proper analysis of the framerate (like with the demo). You come across as a person that hasn't played through Killzone 2, yet. NO reviewer has said what you've said. I'll leave the Killzone 2 part of the discussion at that.
COD4 was pushing one system, but not the other. Remember 600p is not a PS3 centric resolution. With the Z-buffer, etc in COD4, it's JUST enough room to fit into the X360's eDRAM (the only way 60fps is possible on the X360 at that resolution or higher).







