GTX 1070s are still overpriced due to cryptocurrency miners. You can find plenty of GTX 1080s for under $550, so it might be worth getting one of those instead. Or see what happens to pricing now that RX Vega is launching, since Vega 56 should be a bit faster than a 1070 on average, and has a launch price of $399 (whether mining causes that price to skyrocket will be another question).
Also, Intel will be launching their new Coffee Lake CPUs next week, which will feature core i5s with 6 cores, and core i3s with 4 cores, so you might want to wait a bit and see how those turn out, and how they are priced.