I'm intrigued at a dual-GPU setup with only x16 lanes. For the 1070, it probably doesn't make much difference (but could add a tiny bit of latency to VR). But for non-realtime rendering, I could imagine that the Vega could hit a bit more of a bottleneck with a x8 link.
When the Thread Ripper refresh hits, in a couple months, it might be worth a look. If Intel, then probably i7-7820X (28 lanes) or Xeon W-2135 (48 lanes).
Perhaps the next gen of Intel's LGA2066 socket CPUs will be a bit more compelling. I'm hoping for more cores, lower prices, and soldered IHS.