Based on what we have been seeing in the battery life test thread, I would say don't set your minimum below 400, especially if you use navigation (particularly with music). You may even find you want a 600 minimum.
There is more in the mentioned thread.
The issue is pretty deep and you will find a lot of misconceptions about overclocking this phone there.
It's not the size of your overclock that matters. It is how you use it....in conjunction with an appropriate governor.
Don't judge me. I have clock envy.