OK, interesting discussion. I remembered the 300,000lb figure when the 757 was the big topic of discussion about a dozen years ago when it was pointed out that the 757 was intentionally designed to beat the heavy weight class. Perhaps it was the 757 that lowered the bar. The 757-200 has a max gross (takeoff) weight of 255,000 lbs, and the 757-300 comes in at 272,500 lb. However, it seems that in practice, controllers still do not generally refer the 757 as a heavy. I have yet to hear a 757 pilot refer to their machine as a heavy as well.