Long story short, Barnes & Noble released a simple e-reader that turned out to be a full-fledged tablet computer that can run the latest versions of Android (2.2, 2.3, and 3.0).
Default Nook Color voltages:
300 MHz @ 1.0v
600 MHz @ 1.1625v
800 MHz @ 1.3v
1100 MHz @ 1.35v
1200 MHz @ 1.375v
These are the lowest voltages I used without any crashing:
300 MHz @ 0.8125v
600 MHz @ 0.95v
800 MHz @ 1.075v
1100 MHz @ 1.225v
1200 MHz @ 1.3v
I ran StabilityTest and Quandrant Standard to stress test CPU after lowering the voltage.
To feel a little safer, after finding your lowest stable voltage, you could give each setting a slight bump, such as this:
300 MHz @ 0.825v
600 MHz @ 0.9625v
800 MHz @ 1.0875v
1100 MHz @ 1.2375v
1200 MHz @ 1.3125v