I think it will be very difficult to find what you are looking for until the systems are released. Even then, anyone who benchmarks has an agenda.
I would say the most trustworthy folks to listen to at this time are the software companies announcing they will be optimizing for the G5. They will have had enough access to the machines to be convinced it is worthwhile to do so. I think one of the best was the fellow from Wolfram who said they would be positioning the Mac against engineering workstations. That says a lot. Some people will say that's just marketing hype. But, their committment is now a matter of public record. It will be very difficult for them to change their story.
A couple of things to remember: most people do not have the skills to conduct a true benchmark. Decisions have to be made regarding how to set up and run the programs. Look at all the crap being raised over the SPEC benchmarks Apple commissioned, and most of the crap being raised is a bunch of BS from people who don't have a clue what they're talking about.
The other big thing is the functions people use in applications is often quite different. So, whereas an application may be fast for one person may not be so fast for someone else. The G5 killed the Dell box on the Photoshop poster - that will be representative for a lot of PS users, but nowhere near all of them.