Quad G5 Stability Problems / Slowness / Upgrade options?

Question

Well, this is going to be a long post, so bear with me.
First, I'm totally Steve Job's dream. I bought the Mac Mini and it was a complete gateway drug, now I have a brand new PowerMac G5 Quadcore something or other. Okay. I use it for motion graphics work, mostly After Effects, but I've also got Final Cut Studio installed. I've had the G5 for a month now (I know it's almost obsolete by Mactel, but AE and Photoshop won't be available on Mactel for, like, eternity, so I upgraded early.)
So that's the setup. My problem is, the G5 quadcore tower is way less reliable than the Mac Mini was! The thing that impressed me about OS X and the mini was that nothing ever went wrong. I could be burning a DVD, listening to something on iTunes and doing a complex AE render, and Mac mini would figure it all out. I never had to reboot Mac mini unless a software update demanded it.
I've had two occassions now where the G5 tower completely crashed. I'll go over them in details.
The first time, I was using AE and previewing on a camcorder/TV over Firewire. So the set up is, PowerMac -> camcorder (Firewire) -> TV (S-video).
Okay, the first thing I did that might be weird is: I was running activity monitor during my AE renders to see the extent to which 4 cores were actually being used. I discovered to my surprise that even during my most complicated renders, PowerMac was only using 50% of its processing power. It engaged all 4 cores, but each of them never went over the 50% or maybe 60% utilitization. So either AE just isn't optimized, or there's an upgrade I should perform. (See details below.)
Okay, next weird thing. I put PowerMac to sleep with the camcorder still on, and woke PowerMac up a little later to continue working. Now I'd left the camcorder on this whole time. When I went back into AE and told it to preview to the Firewire again, PowerMac froze. I got the spinning beach ball. I thought, "Oh, sometimes that happen, I'll just wait and let PowerMac sort itself out." An hour later, though, I still had the spinning beach ball, so I had to reboot.
A day or so later, something similar happened. I was doing a complex render in AE. I had 20 minutes remaining. Knowing that the CPU was only used to 50%, I decided to watch the latest Channel Frederator in iTunes while the render completed. I turned iTunes to full screen mode to watch Frederator. After about ten minutes of this, I got a freaking KERNEL PANIC! I got weird text dumped at the top of the screen, and a sound sample from the Frederator I was watching was repeating over and over out of the speakers. Unfortunately I didn't think to write down the weird text.
So here (at last) are my questions:
1. Why is PowerMac only using 50% of its CPU during renders? (Bear in mind, AE isn't GPU-enabled to my knowledge. So its renders are all CPU.) My only guess is, that the renders are memory or disk constrained. Adobe does recommend that I get a second hard drive for AE to store its temporary working files, so that AE and the OS X swap space aren't competing with each other. Does this make sense to anyone else? Also, I have 1.5 gig memory, is that too little?
2. What is up with these crashes? This is like Windows XP land. Again, what sold me on the all-Mac graphics setup was the stability of the Mac mini.
2.a. Are there hardware diagnostics or software tests built-in to OS X that I can run to troubleshoot?
2.b. While setting up PowerMac, I copied system settings (and everything else) from Mac mini. I'm worried that there's a configuration file somewhere that's confusing PowerMac into thinking it's secretly a Mac mini or something. Of course, when I say that out loud, it sounds completely silly.
Thanks in advance,
-Paul
Quad G5   Mac OS X (10.4.5)  

Answer 1

1. Only certain filters and effects in AE are well multithreaded and can take advantage of the four cores. I use AE a lot as well, and I can tell you this is normal. What you want to consider is buying the Nucleo plug-in from Gridiron Software at http://www.gridironxfactor.com/products/nucleo_overview.asp
This plug-in will allow AE to fully utilize all four cores on almost anything you're working on, except for effects that are temporally dependent, such as Particle Playground. You need to be using AE 6.5 or 7 to use Nucleo. I bought it and it's one of the best things I could've done. However, your 1.5 GB of RAM is rather small for using AE on a Quad. I'd consider bumping the RAM up to 4 - 4.5GB or so. If you AE 7, it can utilize 3 GB of RAM (previous versions were limited to 2GB).
2. I bet you got the beachball when you returned from sleep because the camera had also gone to sleep and didn't wake up. I imagine that if you'd turned the camera off after waking up from sleep (or power cycled the camera - turn it off and then right back on) the beachball wouldn't have occured or would have gone away. I'm pretty sure I've had this happen to me on my Quad and PowerBook, and this always solved it. Not sure as to the reasons for the KP you got when using iTunes... sorry.
2a. Your machine would have come with the Apple Hardware Test which can be used to test the hardware of your machine. It's on the restore disc that came with the computer. You'l need to boot from the CD while holding down the option key. This will present you with a list of boot options, one of which will be the AHT. For testing memory, I'd recommend using Memtest which you can get a http://www.memtestosx.com For best results, you need to start in single-user mode so that it can test as much RAM as possible.
2b. I did a clean install of all my applications and whatnot on my Quad to avoid a problem like this... It's very time consuming, though. If you're concerned about this, you could delete all the preferences files from the computer and reboot, but you'll then have to reset your prefs in all your apps, and may have reenter some serial numbers as well. In any event, I wouldn't try this unless you start to have frequent issues. My Quad has KP'd once (while using Toast, I believe), but hasn't done so since. My PowerBook has never had a kernel panic.