In pre stages of development, just based off the preview info of screen shots, video and developer feedback, CE3 runs a bit better on the PS3 than it does on the Xbox.
So either it's easier for the engine to run on the PS3 architecture (it would be a first), or a "great" deal more time and effort has been put into the pre-code to see the better results currently seen (seems doubtful).
Either way, the point is that it runs a bit better on the PS3 at the current stage of development.







