the hybrid is a better choice
the x cal comes with a coil spring fork
and it will have a limit to how stiff it can be adjusted
and that limit will almost definitely be too soft for a 300 lb guy
it is possible that there is small difference in the strength of the rims
but that will only come into play if you are crashing into curbs and rocks
which you should avoid
for regular riding the fx bike will be plenty strong
and is designed for exactly the type of riding you said you want to do
also
i am 6 foot five
and i have a bike with a 22 inch seat tube
and the 400mm seatpost i have
which is damn long
is out close to its maximum extension
and i have to be careful that i unweight the saddle over bumps as much as possible
as i have bent several seatposts in that frame
partially because of the long unsupported length
under my 260 lb weight
so consider my experience
add two inches to my height and one inch to the seattube
and eighty pounds of rider weight
in my opinion
if the fx is comfortable for you
then it would be a good choice
if the fx is not comfortable
then keep looking