7700K or R5 1600 (or higher) if buying right now. Since you're comfortable with selling on ebay (Amazon is more lenient on fees but money takes like two weeks) may I suggest
buying this combo and selling the 580. This is what I did. Got $455 for the same 580 after fees and shipping. I only paid $605 for the combo last week. Made the 1700X basically be $150 out of pocket, but yeah you're counting on that sale. Since Vega will be announced in 3 1/2 weeks I'm going to see what it is before buying a 1080TI. Only thing about Vega is the EK A240G AIO cpu/gpu cooler combo only fits for Pascal cards.