Can i download the 100MHz, set it to a 1000 frequency and expect better battery life or is it "one way or the other" type deal?
that must need explaining more. but then actually no one can really say. the kernel i get best battery life with may not be the one that works for you. theoretically the lower the voltage the longer the battery lasts. but setting one to a higher frequency would naturally cause it to run hotter and therefore run up battery faster. so what everyone has to do is try out the kernels to find which one has the best combination of factors. the higher the frequency the faster your droid should run. i think optimum is about 800Mhz. above that you may start seeing problems with videos not playing or other small things. below that and you may experience lag more often....yuo just have to play around with each to see what works for you!
listenman20 is exactly right-there are far too many variables to give a concrete answer. The other question is "better than what?" Stock? Another kernel?
The other issue is how you have SetCPU set up. There are a variety of settings and profiles combinations that can either extend or kill your battery life, but again, those specifics will vary depending on kernel, usage, individual phone and actual performance expectations on your end. I can get great battery life by forcing the phone to run like a laggy dog, or I can set the thing up for pure speed and completely kill the battery. Generally, people set it up for some kind of acceptable compromise between the two, and "acceptable" will vary from user to user. And how you get to that compromise requires some testing and experimentation on your part.
While understanding "How" may get the job done, understanding "Why" will get the job done properly.