As others have noted, the key to high quality LPs is not the weight of the vinyl in and of itself.
I have 120g records that sound simply marvelous. I have 140g records that are to die for. I have 180g records that are stunning. I have 200g records that are great. Basically, one can achieve marvelous sound with any of these weight records. The key is the quality of the vinyl, the excellence of the source and cutting engineer, and all of the critical steps that go into cutting, plating and pressing.
At the same time, I'm very inclined to believe that in identically controlled quality of manufacturing, one can demonstrate a sonic improvement using a heavier weight of vinyl (e.g., 180g vs. 140g) due simply to the bit of mass loading provided. If my recollection serves me, Michael Hobson made this experiment during the early days of establishing Classic Records and demonstrated it at a meeting of the LA Audio Society. He also reported demonstrated a sonic improvement with his one-sided pressings vs. two-sided. Perhaps someone on the board has a link to the article I'm recalling?
At the same time, I'm very inclined to believe that in identically controlled quality of manufacturing, one can demonstrate a sonic improvement using a heavier weight of vinyl (e.g., 180g vs. 140g) due simply to the bit of mass loading provided. If my recollection serves me, Michael Hobson made this experiment during the early days of establishing Classic Records and demonstrated it at a meeting of the LA Audio Society. He also reported demonstrated a sonic improvement with his one-sided pressings vs. two-sided. Perhaps someone on the board has a link to the article I'm recalling?