I would pick up and i5 and stick with the 760 for now. You might have to turn some settings down but it will good enough for 1080p and a new CPU will give you a massive performance boost in a lot of games.
Yeah you can solo all the old content with no problem. I believe you can't do it at 80 due to the stat squish they did a while back. I haven't played wow in a couple years though.