Which goes to show that printf does not support big ints.

You could write

print $result->as_hex();
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because, with the bignum pragma in effect, the numbers are upgraded to Math::BigInt objects which have the as_hex() method (among others).

And to get rid of the "Hexadecimal number > 0xffffffff non-portable" warning, you could say

my $var1 = hex("0x0000805063008357");
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(hex() would need to be imported for perls before 5.9.4)