I’m still using a G5 at work and it’s still fast for Photoshop, although I’m not trying any video. IMHO, at the high end, the number of applications that really demand the latest and greatest keep diminishing.
I have a cheap Core i5 laptop that does 1080P video from my DSLR without complaint. I do most of my basic video editing on my iPhone, which is a far cry from a Mac Pro.
Sad but true (this coming from a G5 owner) - every (Intel-based) Mac Mini put out the last 3 years will lay waste to the PowerMac G5.