Mass delete of registered scam users

Thinking that forcing people to register for my site would help stop the spammers, I made this a requirement. Now I have about 17,000 spam registrants. Since I still moderate all comments, the only consequence of this is the slew of fake users. Unfortunately, this seems to have slowed down the site and I want to delete them. Since most of these spammers use email sites such as outlook.com to generate a fake email address, it is easy enough to spot the fakes. But removing them is a tedious job since WP only shows 20 registrants per page at a time.

I am hoping there is a way to get into the database through another door that would allow me to search for and delete the buggers en masse. Anyone know of a way? I have checked the forums and most posts on this issue are old.

Thanks.