It is a benchmark report by Pfeiffer Consulting. I am sure that it is sponsored by Apple, but it is what you asked for, a comparison between the older machines and the new crop. The older Mac is only a 500mhz, so you may have to guess at the relationship to the previous Quicksilvers.
The PDF was a good read but it's a little bit negative in some ways
I noticed something in the specs comparison page of the PDF.
The old 500Mhz G4 might have only had 3 PCI slots but they were twice the speed of the 4 slots the DDR powermacs have.
I know the new models (and the digital audio G4s and above) have faster PCI thoughput in Mb/s than PCs do (acording to apple) but why drop from 64bit/66Mhz to 64bit/33Mhz ?
surely they'd be in the 430 Mb/s range rather than the 215 Mb/s apple claim they have if they'd kept the PCI clockspeed the same when they improved the system controller (or whatever controlled the PCI slots on pre DDR models).
Also, the benchmarks in the report don't look too promising :
The dual 1.25Ghz model is 189.1 % faster than the 500Mhz G4.
2 x the cpus, 2.5 x the clock speed, a faster system bus and 4 years of progress. It isn't even 3 times as fast.
The dual 1.25Ghz model is only 16.2 % faster than the dual 1Ghz model.
The dual 1 Ghz model is 43.4 % faster than the dual 867Mhz model.
That seems very impressive but Barefeats reported it as being 20.8 % faster with their MP action file test. I can only assume the faster system bus on Ghz model accounts for a lot of extra speed when running filters and actions that arn't dual cpu aware.
Illustrator / Indesign
All the tests showed the dual 1.25Ghz to be 2 - 2.5 x the speed of a 500Mhz G4
This is nowhere near impressive given that the dual 1.25Ghz should be 2.5 x faster before it even starts using the second CPU.
Personally speaking I'm waiting for Accelerate You Mac! and Barefeats to conduct tests of their own on the dual 1.25Ghz model before I take the collection of overly negative and overly positive results in this particular set of benchmarks as completely accurate.