Well it goes like this:
IBM designed to power970 for Apple to use in it's computers and provide a lower-end solution for stuff like blade servers as a alternative to it's power series proccessors.
It's designed to scale up to around 16 proccessors (IBM is suppose to be developing 4/8/16-way workstations) and probably has quite a few technical simulaties with AMD's opteron since IBM helped out with that one, too.
AMD has a edge on the G5 in terms of pure performance, however Apple isn't tied to backward compatability with older platforms like the x86 stuff, so has a better performing platform for the cpu.
In Apple's high end power mac.
Each Proccesor has it's own bus to the motherboard controller. These busses operate in ddr mode and at 1/4 the speed of the proccessor. So with 2 cpu's you have 2 channels operating at 500mhz with a effective ddr speed of 1ghz. 8GB/s bandwidth for each proccessor for a total of 16GB/s.
(In a x86 smp system you share the single bus to the cpu.)
For the memory it has 2 200mhz channels going to it. That way with 2 banks of RAM each cpu can access the memory similataniously. Much like the nvidia dual channel stuff. They are ddr, of course, so a effective speed of 400mhz. Both channels together have a total of 6.4 GB/s of bandwidth.
If faster cheap memory was aviable and the chipset supported it, it would make the G5 that much more powerfull since the cpu's have so much bus speed aviable to them. (I am guessing)
8x agp slot...
IT has a "2 16-bit 800MHz HyperTransport interconnects" for the on-board stuff:SATA HD controllers, Firewire, USB, Gigabyte ethernet, Optical/Analog audio. 3.2GB/s bandwidth for all that stuff. (all the newest protocols of course)
It has a couple 133mhz PCI-X slots in addition to the normal PCI (33mhz) slots. For a bandwidth of 2GB/s(combined) compared to 266MB/s (or Mb/s?) for normal PCI slots.
All that crap is aviable from Apple's own website.
I suppose this all means that the PowerG5 can move lots of information around much faster then a normal x86. Now if the CPU/memory stuff can utilize it, that would make it a Intel-Killer in terms of raw performance. Still needs some catching to do in the mhz department, though. Technically the G5 is a nice modern design with the latest stuff.
I think that it may be superior when doing a lot of multitasking do to the dual cpu design, and in things that require much I/O speed, like video editing. But that's just speculation.
Personally I would love to have a powerG5
If you compare it to other pre-built computers like the Voodoo F-class (64bit amd fx-51 $2700) it is priced very competatively.
Then it becomes a question of what you prefer. Windows or OS X. I am a Linux user so It's nice to have the ability to run in 100% native 64-mode in AMD64 platform. (SuSE pro
$79). Also can run well on the PowerG5.
ALso something going for the Apple's in the quality of build for the computer. The guy that designed the case is suppose to be a industrial desinger genius. The 9 fans keep everything cool and the entire computer is suppose to be sub-whisper quiet. The way the air flow is designed to keep the enterior dust free.
I'd bet that the FX-51 still have a edge on raw performance, though. Also x86/windows is the way to go if your a big gamer.