Seems you're asking at least 2 diff questions:
1. Relative merits of FA vs SW model Stellas
2. Relative merits of various models w/in those lines compared to each other--e.g., 10,000 vs. 14,000 vs. 18,000 vs. 20,000
The former has been explored already; and, Hatidua may have already beat the Smithsonian to the rest of the offshore FA's.
But, the latter question lingers. What are the respective rationales for the different models? Is this just Shimano chutzpah? (we're so good at teasing you with products we don't have to say--much less explain--anything)? I'll assume for now the different lines reflect different engineering trade-offs re weight, drag, line capacity to optimize some different types of fishing. But, I can't tell which and don't expect Shimano to explain it--I haven't seen a word on this from them.