At home my HE tunnel is snappier than the plain ipv4 from rr. The weird thing is it is not just a case of user perception (mine). One of the upstream s1 ntp boxes I sync with has ipv4 and ipv6 and is relatively close. I set one of my s1s to sync with both the ipv4 and ipv6 addresses of the machine and the ipv4 clock displayed a lower delay and less jitter while the offsets were seasonably close.