>>30318
2.1 Give a very hard captcha every post during the ratelimit.
2.2 Fully block "brand-new-ip" posters.

It prevents immediate ban evasion for more than 3 times per row. Normal users don't rotate IPs 5 + times per hour. So a spammer in the worst burns 3 IPs if the limit is 3 IPs per 1 hour.
If possible, bypass "known" IPs that posted at least once last week OR IPs that have captcha bypass.