I think it's a hit or miss on how some guitars react to the mass of a stoptail. Maybe, even between two of the same guitars.
Case in point: A long time ago, my old 70/71 SG Standard was modified from it's original Vibrola to a stoptail that I think was made from zinc. A couple years later, it was suggested that I try a lightweight aluminum stoptail for the purpose of adding a bit more chime and sustain to the guitar's natural response. I did not notice much of a difference at the time. No big deal, cuz the SG sounded pretty darn good after I finally found the magical pickups that complimented this guitar.
Then just a few years ago, I read at another forum about this same subject on switching from aluminum to a solid steel stoptail to counteract a "wooly" guitar. Enter Philadelphia Luthier Tools & Supply with their Precision Machined Steel Tailpiece. This type of stoptail made a difference... a difference for the better at least for this guitar!
The aluminum tailpiece that Robert posted shows a weight of 31.5 grams. In comparison, the solid steel stoptail on my old SG is 3.3 ounces, or 93.5 grams... almost 3x heavier. And, NO NECK DIVE!