Originally Posted by Aeternus

The only thing that would be worth it would be the point at which your soul ceases to be useful: The point at which the final iteration into the Prime has been made. Containing the sum of all knowledge, all experience, and all emotions, it would cease to be able to grow or improve itself. At that point, you cross into godhood. Should another entity be able to grant that, it would merely... speed up the process.

Yet not even "the devil" could grant such I think, seeing that that being has some learning to do himself...