I mean I have had pretty good results with battery life, mine has been pretty constant, if not a little better since moving up to 4.4.2, then again I am not using a heavy customizable ROM like HD8.
However, with the new firmware release, you should just flash it over via Odin and be good to go, it's just an update, shouldn't require anything else. You shouldn't need to factory reset. If you wanted to clear the dalvik and cache that might not be a bad idea.
I know that for good measure in my guide, I suggest to flash the firmware each time via Odin, while not necessary I just know it made the ROM, from my stand point, slightly more stable
. Flashing the firmware again won't hurt anything, it only has the ability to make things slightly more stable, or just do nothing lol.
The Kernel is how the hardware talks to the software. Updating the Kernel can do a lot for the device in terms of performance and battery life. It can be good or bad, so who knows how that would work out for us.
I am very content on staying with what I have right now. I haven't had the data drop issues like many others have had yet