So realistically we still need 64 bytes to store each known key pair
I disagree on that, you don't exactly need private keys to be handy, you need them only in the very rare occasion the attack was successful for the final printout of the found private key. They can be on the tape or something. Only the 1/2 of the data, 32TB with X coordinates have to be on the fast RAID.
32 TB on tape
?DAT 160 = 80 GB uncompressed (160 GB compressed)
DAT 320 = 160 GB uncompressed (marketed as 320 GB assuming 2:1 compression)
Cheep and ultra-reliable, you need less than 100 of them for this database. Whoever tries this in practice won't have a problem to buy 100 tapes.
Edit:
Just found out there are 6TB models now:
http://www8.hp.com/us/en/products/tape-drives-enclosures/index.html#!view=column&page=1
Had no idea that technology advanced so far in a few years.