Assuming there's no impending disaster, I say take down the plaster and lath with a coal-shovel type of shovel, and perhaps with an ice chopper. The shovel actually removes the stuff in 'sheets' as you run it along the wall, more or less. Then, once you see the exposed insides of the wall, you'll be able to see if the sawzaw was a good idea. There may be piping or wiring or cable or something in there that would be disasterous if cut, sight unseen.
Overall, do your demolition in small steps. As much as you want to get done quickly, it's not the way to go. Make sure your return ducts (if any) are closed off too.