If you are OK with doing an OC, get the 1600. You'll end up in about the same place, +/- 3.8. If you get a good 1600x, sure, you'll hit 4.0 or maybe 4.1 but that's all luck. I have no doubt I can push if not top 4.0, but I just don't "need" to.
At the price range, and having a nice AIO, I'd...