Hmm... I wonder if the fact that there are currently 200 guests and 45 users has anything to do with the site's performance. I looked at a few of these new "users" and it looks like they might be spambots that just haven't posted anything yet.
It's going to be a big factor, but likely not the actual cause. A well-run site should be able to handle this sort of traffic without any major issues. Reducing the bot traffic would likely help things temporarily, but that's not really the way to solve the problem.
Also, the reason so many spambots register here but don't post is that the spam prevention used here doesn't really target registrations. The solution at tfes.org takes a very different approach - we try to stop spambots from registering, so we don't have to worry about them trying to post.