I haven't noticed a difference in battery life rather I throttle back or speed it up, but I do notice differences in performance. When you add all of that up, that is why I keep mine set to 528/528 all of the time. That being said, I stand by my original disclaimer: "Your mileage may vary."
I say that because, for me, it's a no brainer. The cpu is rated for a specificity of 528 mhz, so I don't see it as being overly "dangerous." I notice that setting the min/max values both to 528 renders the best performance, and I haven't noticed a hit (if there as been one, it's been minimal enough that I haven't taken notice) in battery life. I also noticed that when I set the minimum speed to 128 and kept the maximum speed at 528, I did not notice an increase in battery life either, but I did notice less performance than when both were set to 528.
Now, I don't have a cheat code that has unlocked the G1's debug menu allowing me to access "God mode," but I am pleased with where it's at. So, I keep it that way, because I'm the one who has to use it. I'm not making promises to anyone that they will observe the same findings I have, which is why I think that if they aren't afraid of the risk of "overclocking" that they should play around with the settings and find out what works best for THEM and not worry about what works best for JaceMan or DaYuMu.
My 2 cents!