If abuse is an issue, why not hash the IP with a nonce?
If you don't know the nonce, you can't match against other users-- so not useful for abuse.
But I'm skeptical re: abuse uses. For commenters, sure-- you may need to store IPs to combat abuse. But for readers? At most you would need sampled data or in-memory counters (e.g. to catch high volume bots).
Unfortunately, there really isn't any penalty for failing to minimize private data collection.
Also, by removing unlikely candidates (IPs owned by irrelevant entities or that are not US based) you could get the search range much much smaller, and with the FBIs budget you could probably compute it all in a few days even with a 1-second hash time.