How do you plan on getting the captured files from the G5 to the MacPro?
[Robert Ober] “I still am curious about offline workflows that involve HD to offline. Such as captuing ProRes and working in DVCPRO HD or similar. “ That is not how offline/online works. You edit in the codec you capture in. If you need to same space or are doing a multicam project on a slower system or drives you might capture offline as DV25, do your edit and then you recapture as HD ProRes your final timeline. With the speed of the systems and drives these days and working with DVCProHD or ProRes we don’t think in offline/online editing, the original captured codec is used throughout the entire process.
I have used software RAID for years, I get over 400Mbps from 10 drives striped together. I have a manual backup scheme still have a safety net back not a keep on going if you lose a drive but I can build a 10GB system for under $2500. If you are doing only a couple of streams of DVCProHD or ProRes you should be fine with 2 or 3 internal striped drives.
Maybe I have overlooked this but I cannot find what HD decks/format you are using.