I'm replying to bump this because I have been having this issue for about two weeks now. Some times it gets so bad, I switch over to Chrome. I'd like to hear if anyone has a solution to this.
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Well, now I am replying with a fix. I found another thread talking about this, and the fix was instant! All you have to do is clear the cache for Safari.
If you haven't already, enable the Develop menu item in Safari by going to Safari Preferences > Advanced and tick the box "Show Develop in menu bar".
When it appears, choose the Empty Caches option. CPU usage returned.