MDD "Firewire 800" Freeze-up issues?

[RagnCagn]

I'm have a couple of questions regarding problems with a MDD, "Firewire 800" that I've rebuilt.

The "current" configuration specs for the MDD I've built are these:
1) Dual 1.25GHz
2) Motherboard is Apple part number 630-4633 (Note- This is the original "Firewire 800" motherboard that it came with. According to the serial number and ID sticker, it was originally a single, 1 GHz. I swapped out the processor, and bumped it up to the dual 1.25GHz.)
3) Pioneer DV-105PD DVD Superdrive
4) Video card is GeForce 4 MX (64MB)
5) 1.5 GB DDR333
6) OS 10.5 installed

The system is experiencing "Freeze-ups" similar to those you might see with a processor overheating issue. However, while the heatsink gets fairly warm, which I understand is normal, it doesn't seem to be overly "hot". You can touch, and remain touching, the base plate area of the heatsink and not get burned. It just gets pretty warm is all.

My searches at "Apple" shows that in the Original configuration (Single 1GHz processor) the system ran at 133MHz bus speeds, but that the Dual 1.25GHz ran at 167MHz bus speeds.

Question 1: Is the bus speed of the MDD determined by the processor, or the motherboard? I always thought it was the processor. Is my model "Firewire 800" motherboard (Apple # 630-4633) compatible with either 133MHz Bus or a 167MHz Bus speed?

Question 2: There were several processor heatsinks for these models. The one I'm using is the Stainless Steel one, and not the Aluminium or Copper. I can't seem to find if this one is compatible with the Dual 1.25GHz processors. Do I need to change the heatsink to different one, and if so which one should I use?

Just as an added note, this system has sometimes run normally for hours without freezing, but it has also froze up within minutes of starting it up. The only thing specific that will force it to freeze is attempting to burn a DVD (heavy CPU usage). However, it has also frozen-up while just surfing the web (light load conditions). Any help or ideas with resolving these issues would be greatly appreciated. I thought I knew most all the Apple G4's pretty well, but this one has me stumped.

Thanks in advance!

RagnCagn