The 6.4L comes with VCT, MDS and a plastic intake manifold (or composite as they call it). It has rubber valve seals that will more than likely blow when boosted.. Also has higher compression ratio which will hurt boosted performance. Does it make more HP? Yes. But I still would not own one..
A crate motor 6.4L or 7.0L is a lot better than a factory 6.4L.
As far as the srt8 jeep goes, the 2012 with a 6.4L is slower than the 06-10 body style with 6.1L.