Thanks for your input, Hockeypuck25! Was the wall mount plate you drilled through a Monoprice mount? The steel on my mount (Monoprice product # 8587) is pretty tough, but I only have bits made for wood (and concrete, but that those slide right off the metal). I was barely able to put a dent in the plate after 10 minutes of high-speed drilling at it.
Do you or anyone else have any suggestions for extracting a M8x90 lag bolt from half an inch in the wall? I bought an extraction kit, but like the mount plate, the bolt's steel is too tough for me to drill a pilot hole into the center of the broken bolt. I'm hoping a good metal drill-bit set will also aid in this in addition to possibly trying to drill a new hole in the plate.