You didn’t say what kind of G5.
I have edited lots of DVCPRO HD on a G5 dual 2 GHZ. It works fine.
Editing and delivering 4:4:4 is silly. DVCPRO HD is not a 4:4:4 codec. You would be just making really huge files with no improvement in quality, as the compression happened in camera before you captured it. If you have a massive fast disk array, you can probably do it anyway, if you are hell bent on it.