Just a note to Asus P5K/P5KR and also looks like it affects P5B as well:
If you are experiencing the following symptoms:
If you are overclocking your PC
i) Your Prime95 is stable
ii) However you experience stuttery game play and frequent crashes in games.
iii) Your PCI-E link width shown in CPU-Z or Nvidia system Info shows bandwidth at only 1x (sometimes upon a reboot it'll show back to 16x but will be unstable).
iv) Your audio has static on it.
This is a common bug and there have been many proposed workarounds (all which I have personally tried).
What worked for me:
a) Go into your JumperFree configuration / Advanced / Northbridge Voltage and set it AT or LOWER than 1.45 V
What didn't work for me:
a) Altering PCI-E frequency in BIOS
b) Upping Northbridge voltage
I also experienced a vdroop with this motherboard which I will deal with in a separate thread.