Getting the RX 460 or the 470 isn't the point if both will be bottlenecked by your CPU.
One will have more extra power remaining while the other some less extra.
If you can, get the 470. Whenever you have the option, switch the CPU for a better one, shortening or erasing the bottleneck on the CPU side.
If you invest a little more now, you won't have to change the GPU again later on when you change the CPU to match it's performance.
And, you can even use some settings in-game to make it be more GPU heavy so the CPU won't have so much load on it, gettin rid a bit of the bottleneck as well