Yes the stock heatsink is not designed for fanless operation. Even at base frequency and lowest voltage you risk overheating with no airflow.
Keep in mind those little fans have about 2cfm coming out of them, so you can easily get a ultra quiet 120mm fan and that will provide more than enough airflow at close range to keep it cool with very little noise. If your going this route I wouldn't do it unless you have a heat gun and can directly measure the temp of the small heatsink on the top (should be under 80c max).
Keep in mind those little fans have about 2cfm coming out of them, so you can easily get a ultra quiet 120mm fan and that will provide more than enough airflow at close range to keep it cool with very little noise. If your going this route I wouldn't do it unless you have a heat gun and can directly measure the temp of the small heatsink on the top (should be under 80c max).
Thanks for the info, I was thinking (for the other guy) that one may get away with it at lowest core/mem voltage/freq but I believe you if not. Yes I will get the IR temp meter from work, currently I am measuring anywhere between 30-40degs on the heatsink that is on the component side of the PCB (other side than stock fan), that's at 832Mhz. I have some others at 900Mhz but can't measure those as easily without the gun. I assume by small heatsink you mean the one that is where the minifan is?
This is in fact what I enjoy soooo much about the MLD2, the way we can tune and customize and play with it. That's just so much fun and awesome. So, great job!!
Others can probably pitch in here too with their views.