The import option in LOG AND TRANSFER now has AVCIntra Native as an import option....so importing that is fast, and lighter than ProRes. BUT...you cannot have an AVCIntra Native sequence. Odd, but true. So you can import AVCI, but your sequence settings should be ProRes and you will be rendering to ProRes.
Or get the great tools from MXF4QT or Calibrated or Raylight and edit the MXF files natively, without the need to import.
The reason why it's roughly the same speed of RT as ProRes is because it is ProRes.
Final Cut now knows how to play back the clips in the timeline, but any changes will be rendered out in ProRes since there is no way for Final Cut to write new AVC-I video, it's just too intensive. So Apple's claims of native AVC-Intra editing is kind of a half-truth. The footage is native, but transitions and other new elements are not.
[Hector Silva]"The reason why it's roughly the same speed of RT as ProRes is because it is ProRes.
No, it's not. The clips that are being decoded are AVC-I, the are just not getting reencoded to AVC-I. So basically, you are playing a different codec within a ProRes timeline. So it's not exactly ProRes (unless you choose to transcode to ProRes in log and transfer). If you put an AVC-I clip in a ProResHQ timeline with no transitions or effects, the render times are very fast.
[Hector Silva]"The footage is native, but transitions and other new elements are not. "