Not true for all games, and this is why I dislike blanket statements like this. Sure *some* games may run at 144fps, but its not a guarantee. This applies for both AMD and Intel, so don't think of this as Ryzen hating, I'm just trying to bring some level of realistic expectations back into this thread. Ryzen definitely won't hit 144fps on AC:O, or PUBG, or BF1, not even a 8700K @ 5GHz will do 144fps in those games.
What about the latest AAA title, Far Cry 5? Nope, won't do 144fps there either:
http://www.guru3d.com/articles-pages/far-cry-5-pc-graphics-performance-benchmark-review,8.html
To the OP, I would suggest either a Ryzen 2600 (wait for launch reviews to confirm performance) or i5 8400 if your CPU budget is around $200 or less. If you can afford an i7 8700, then do so, you won't notice it today on your 60Hz panel but if you ever do upgrade to a higher Hz panel (or upgrade your GPU in future) you will start seeing a difference between it and the cheaper CPUs.