Man, I am half lost with this one so let me slash at the bushes a little. (just like fly fishin
)
Jumbo tosai could result from the freakish combination of jumbo parent genetics with ideal conditions and all the luckiest timing and weather.
Jumbo tosai could be tobi seperated from the spawn to grow elsewhere.
Jumbo tosai could be the result of heavy early culling to maintain lowest stocking densities and greatest growth.
Jumbo tosai could result from growing on in the fully heated greenhouse ponds producing a two season growth fish in the first year.
Jumbo tosai could be small nisai.
Advantages? Uh, they're bigger.
Disadvantages, they're XXpensive. Because of the different ways to get a jumbo tosai, different outcomes should be expected in the pond at home. And if they are tategoi they are still in Japan. (or England
)
Is this a question about whether jumbo tosai grow to be bigger adults? I think that may be what would make them most valuable, the certainty that it's gonna be big. But I don't think tosai size can be that certain an indicator and, saying that, I am now out of my league.