See I understand this, but Bizarre is located in Liverpool, UK, and Turn10 somewhere in America no? I don't know how easy or convenient that would be, and Bizarre already has a studio, which I presume MS can just take over. It isn't the same studio as when they worked on PGR though, I believe.
That's why I think the two studios working together to allocate different resources could be optimal. Stuff like recording engine sounds and whatnot could be much cheaper since you've got men on both sides of the ocean to collect this stuff. Has there ever been an example of this kind of dual-studio setup working in other games?
PGR4 is a technical marvel. It's one of the most beautiful games on Xbox 360, period.