I am in New Orleans (zone 9)
and have several seedlings growing from seed.
one is a Florigon about 5ft tall. i plan on putting it in-ground in the spring.
that way it will be well over 6ft (maybe 7 or 8) by winter.
The florigon took 28F temps last winter in a container
with only minor leaf damage.
i had 2 seedlings about 1ft tall i planted in ground... both died.
The Champagne mango (really Ataulfo) are usually in stores
in the winter (Jan-Feb) from Mexico.
They taste good, and from what ive heard grow true-to-seed.
i have several from grocery store fruit., mostly 2 or 3ft
i may plant all in the spring and hope 2 or 3 will be strong enough by next winter to survive.
ive learned to try and protect plants in winter
either by frost cloth, or, by planting evergreens next to them
(just dont let them block out sun)
also, if you can, raise the ground a couple of inches.
this lets the cold air flow downhill.
i plant papaya next to a south-facing wall (my house).
the roots are not a problem, mango might be however...
large rocks,, even 5gal buckets of water can hold in heat from the day
releasing it at night.
there is a report that the variety "Bailey's Marvel"
is more cold hardy than others.
this was one guy however, and has not been verified.