Well written, Nim; without actually doing a bucket test of sorts, it is impossible to know who is larger. Photographs can be deceiving because of the substantial 4" height difference and the difference in breast shape; a cross between fake and natural and the other obviously fake.
At one point on this thread in 2/2011, Beshine stated that she had the fluid drained prior to a fill-up and measured 8000 and 8300, then filled them to a matching 10k; there was no doubt it was a substantial increase because her breasts retained the strained shine prior to and then throughout a lengthy vacation. If we accept her at her word that she was 10k at the time, and photographs would support that figure in comparison to other big implant girls, photos make it is quite obvious that over the next 4-5 years, she progressively got bigger. Exactly how big is subject to speculation, because her breasts are not totally spherical, but more like partially filled spheres, and finding photos where a known dimension is at the same distance from her breasts is difficult.
Like you, I tend to ignore advertised numbers; chest measurement, weight, and bra sizes; even at 10k, Beshine's sport bras clearly had a band size far larger than 34" considering the maybe 4" gap between the band and her chest, but then again, she wasn't using them for support. It seems like much of your computations at the time were from using bra sizes, which again, is subject to scrutiny because of possible exaggeration, and the difference in fit, because both girls breasts, especially Beshine, project very high above the cups. The other problem I see is that, for whatever reason, you appear to be using Beshine's 2011 10k numbers, when, comparing photos from 2011 and 2015-6, show a unmistakable difference in size.
I have read a lot of conflicting numbers from various sources attesting to Chelsea's size at different point. At 5'2", her breasts always look huge, and I agree, the shape and position can add to that appearance. And there is no volume calculator for the shape of her breasts, but if she were standing next to Beshine when she is at her biggest, she would likely have the appearance of looking large, mostly because of her height.
I have never really debated who is larger and would suggest they are very close, but have tried to estimate Beshine's volume based on photographic evidence, yet nothing is definitive because a ½" difference in diameter can make a big difference in volume and though her breasts may be argued as resembling partially filled spheres, they are not perfectly round, so it is nothing more than a educated guess. Certainly who is actually bigger at this time is not worth arguing about anyway.
The issue is how much weight could either bear. I contend that when the weight is affixed to the body, it is easier, and the person more attuned to carry it, than we may speculate. I have read about a case of gigantomastia where the breasts weighed over 120 lbs. total and the person was mobile. Again, it is advertised numbers, but Annie Hawkins-Turner is said to have 130 lbs. breast weight and that may be true. So I have reason to doubt someone saying that a obviously fit Beshine could not possibly carry 80 lbs. Just my 2¢