105 cm Beuchat Marlin Carbone band question

What diameter shaft are you using?

It should be good. You can make fine adjustments with the length of the wishbone if the gun has a little too much pop.

IMO, 2 5/8 bands is a bit excessive for a 6.5mm shaft.

Personally, I like:

for 6.5mm & 6.75mm, 1 tight 5/8" or 2 9/16"
for 7mm or 9/32", 2 tight 9/16" or 2 loose 5/8"

The gun's barrel stiffness should be more than adequate, but the shaft may whip.

1 5/8th, and one 9/16 might be a good compromise.

Excessive if you hit a rock up close, the tip of the 6.5 will bend. With longer shots the 6.5 loses momentum quickly. But we have a lot of fish here that are not on the bottom, and sometimes require range and penetration. You can always power down.