Country blocking – to update to premium or not?

I am getting a bit fed up with 100s of Chinese and Ukrainian hackers attacking my site daily, so I started thinking about upgrading to WordFence Premium in order to do country blocking – my target visitors are only in US and Canada. The dilemma here is performance trade-off, hence my question to those who did country blocking: when you implemented country blocking how much of performance hit did you get? Is your website loading time 10% slower, 20% slower, 50% slower than before?
I was recently reading about country blocking technique using IPSet/IPtables and people complained that they got huge performance hit when blocked China or Russia (on every HTTP request you have to check the IP address against the big list of country IP ranges). And this technique is done on Apache level, so doing these lookups in the WordPress plugin is going to result in even higher performance price… Any feedback here?