Hi Mark,
Thanks for the advice. Good to know, I wasn't aware of the toll it took on the server. I've figured out the feature to block IP ranges based on WHOIS searches on single IP's. Great feature, I've moved all the blocked hostnames out of WP Ban into WordFence blocking by IP range. Works fine!
I have also purchased tar, feathers and cheap headphones, ready for the shitstorm to come. That being said, perhaps it might be a good idea to more prominently feature this functionality -- or maybe even streamline the process in WordFence to make it more accessible for less knowledgable users.
But again, thanks a lot for the advice!