I opened the wallet and bought a MacPro 3.0 GHz, dual duo core, 4Gb, and an extra internal drive for streaming the beast...BFD. I use to have a G5 PPC 1.8 dual.
All system overload problems are gone. I can use tons of high quality plugs all over the place, play them back while tracking without freezing a single track, and I'm only using about 1/3 of my total CPU power. HD hits don't even register on the meter.
Observation: On my Mac Pro the CPU load is always spread over the 4 cores, not evenly...but all four cores are engaged to a degree. There is no single core maxing out.
I'm think one of the problems with the PPC systems is that the cores were not properly threaded. It appears there is a margin of CPU power reserved for system functions. If you exceed the margin for a single core, even for an instant, the system overload kicks in before the second core kicks in. Since the threshold can be exceeded in an instant, it may not be picked up by the meters which are likely averaging, i.e., low pass filter. This may be why people are getting system overloads even when their meters show 50% power available in one core with the other core maxed out.
Just a theory. Bottomline, its worth switching...although the 8 core would have been even better, and my 4 core is now $700 cheaper.