[Brandon Morris]"Can we transcode in FCP to ProRes 422 or 444?"
If you shoot to P2 cards...yes, but after you import as DVCPRO HD. That camera shoots DVCPRO HD, and that is 8-bit, anamorphic...not 10-bit. You won't really gain any quality by converting footage shot as DVCPRO HD. If you take the SDI out and into a computer with a capture card, yes, you can capture as full raster 10-bit...a MUCH better quality image.
[Brandon Morris]"I can't seem to find any comparisons of p2 vs uncompressed sdi footage."
Shoot some. Testing on your own is the best way to see this.
[Brandon Morris]"How big of a difference is shooting via SDI to FCP?"
BIG! 10-bit, full raster...much better than what the camera records.