ipv4 vs ipv6 can go over different peering/transit links, in terms of raw processing speed, at least on consumer equipment ipv6 should be faster because it doesnt have NAT as a requirement, although been on aaisp with your own ipv4 block its possible you not using NAT for your ipv4.
I have had times ipv4 is lower latency to the bbc than ipv6, and I have had times its the other way round. Right now ipv6 is quicker to the bbc for me. Note this is just to the bbc, to another destination it may be the other way round, and yes currently on this machine ipv4 is preferenced.
F:\Users\Chris\Downloads\NEW\undefined\hashcat-3.6.0>ping bbc.co.uk
Pinging bbc.co.uk [151.101.0.81] with 32 bytes of data:
Reply from 151.101.0.81: bytes=32 time=9ms TTL=60
Reply from 151.101.0.81: bytes=32 time=9ms TTL=60
Reply from 151.101.0.81: bytes=32 time=9ms TTL=60
Reply from 151.101.0.81: bytes=32 time=9ms TTL=60
Ping statistics for 151.101.0.81:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 9ms, Maximum = 9ms, Average = 9ms
F:\Users\Chris\Downloads\NEW\undefined\hashcat-3.6.0>ping -6 bbc.co.uk
Pinging bbc.co.uk [2a04:4e42:600::81] with 32 bytes of data:
Reply from 2a04:4e42:600::81: time=6ms
Reply from 2a04:4e42:600::81: time=6ms
Reply from 2a04:4e42:600::81: time=7ms
Reply from 2a04:4e42:600::81: time=6ms
Ping statistics for 2a04:4e42:600::81:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 6ms, Maximum = 7ms, Average = 6ms