2. Instability. Bluescreen at startup is a sign of major instability. Even more major instability is shown by the computer not booting at all. To ensure full stability, run Prime95 for at least 8 hours without errors.
3. See question 2. You could also get a bluescreen just randomly. In games, for instability of the CPU, random squares of colours that aren't supposed to be there are a sign of instability.
5. Not necessarily. You could change the DRAM multiplier instead. Lower it to make it run within specifications. There is probably something similar with the QPI. I recommend you lower them first anyway, then see how far you can push the CPU. Then lower the CPU to stable. Then increase the other multipliers one at a time and see how far you can push them stable. You will need to run memtest86 to determine RAM stability.
Hope that helps. Any more questions or if you need clarification, just ask.