DNSBL caches and IPv6, again

As I've mentioned a few time, I'm trying to figure out the cache behavior 
of DNSBLs, so we can try and predict whether IPv6 BLs would make the 
DNS melt down.

If I had traces of [IP,timestamp] from some medium sized mail sytems, I 
could do some cache simulations.  Medium is in in the range of a million 
connections a day.  Anyone have access to one of those?  Nobody has IPv6 
mail at that scale yet, but IPv4 would do fine for this.

I don't need to know whether the connection was for real mail or spam.  If 
you consider the IPs confidential, hashes or tokens would be fine so long 
as the same token consistently corresponds to the same IP.

R's,
John