I have little to do with video editing but I like to use mathematica. You can see how even the lowly mac air (1.4ghz) will beat the pants off of any G5 here:
http://pohl.ececs.uc.edu/~mark/air_MathematicaMark8.pdfI bet the slowest mini of the current generation will beat the fastest quad G5 for anything. Next generation's i-series mini (and probably thunderbolt as well), even more so. an imac will run rings around it. You'll get modern software (with proper support for your sony handycam and it's avchd, aj) and a warranty, and an up-to-date os.
Of course, a powermac is more intimidating/beautiful/bigger than a mini would be sitting on the desk, and it "isn't intel". I also like my bizzare architectures...
Time the systems running the software you want with video from your camera and see which one works out faster. Then decide if the coolness of the G5 is worth the tradeoff in speed and support of a new mini at about the same price. Or an imac.
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