I would leverage Cloudflare, and block certain countries from able to login/register.
Use Xon's addon to block some VPN's.
Require each new member to be approved, and watch 5 or so posts and look at the IP's of each post.
If the IP's are all over the place, you can ask the user what the deal is...
What type of experiences are you looking for with performance?
I haven't measured anything, but multiple forums, it's working well, and I believe it's running on macrumors as well.
So depending on your setup it could be different.
@021 Thank you for the update!
Is there a chance you can help...
I have some old forum urls from a previous vB4 install.
How could I replace the urls with the updated redirected urls?
I have moved the forum to the root folder now
so it would result to domain.com/threads/173113/