For those that care, see my sig. That is what I'm running and I've noticed an improvement over battery life. I am not using setcpu either. As far as temps goes, I have no idea. Other then it doesn't "feel" hot. But for those that want to know what stock kernel does with 2.2. I'd have no remorse telling you that it runs faster and extends the battery at the same time.
But I think that could also be because I am launching my apps quicker, jit is doing it's thing, and I have picked up on download speeds from 3G somehow (guess baseband update did that) that I don't have my screen on as much. Even w/ more use out of my phone (by simplying playing w/ froyo) I still get longer battery life between charges. And my definition of between charges is once the phone kills itself, do a full battery charge, and remove from charger.
I will not say how many days I can go off a full charge as my definition of use and yours is different.
Yes, base kernel clocks in at 600Mhz when booted without a script or SetCPU. Since 600Mhz under 2.2 is roughly equal to 1000Mhz under 2.1, you will see the same speed but much better battery life.