Prime95 testing is important but it is only testing your CPU when it is fully loaded. At full load, the maximum multiplier will decrease and it might decrease significantly if there is any thermal or power limit throttling going on. Try doing some part load testing. When running Prime95, try running just a couple of threads. The built in TS Bench will also let you run a partial load like this. Make sure both of these tests report zero errors.

Any BSOD while under volting is a pretty good sign that the voltage you have selected is not adequate. It is not unusual for a person to have to reduce their undervolt. The CPU needs to be stable at full load, part load and idle.