The fuel brand is not necessarily the problem. I have yet to see a BGX run well unless it had on-board glow that is on most of the time. If you are going to try the PM fuel, try the 5%. Last BGX I had did'nt like much more than 5% fuel from the best I can remember. Don't blame S&W for a bad running BGX. Thats like blaming Mobil fuel for a bad running AMC Gremlin or Pacer.
220 to 260 is not hot at all, in fact that is a bit on the cool side.