The CPU would bottleneck it at most resolutions, but I'm not sure about 1366x768. Probably you'll still get a high enough frame rate that your monitor is the bottleneck.
You do need to understand what a bottleneck means, though. It's the component that's limiting your performance. What this means is that if you put an RX470 in the system and the CPU is the bottleneck then the RX470 performs no worse than an RX480, or a GTX1080, or even a Titan X.
What this means in practical terms is that an RX 470 might also be no better than an RX 460. It ultimately comes down to price: if you can find an RX 470 for less than an RX 460, then go for it. If you can't, then under the idea that the RX 460 is the same as the next lower tier card then you could replace it with that. At some point this needs to stop, though, because you'd argue that your current GPU is already the most that your CPU can handle which implies that no upgrade is sensible. It sounds like you're using integrated graphics since you have an APU, and if that's the case then you can certainly upgrade to discrete graphics I'm just not sure if the RX 470 or RX 460 would be distinguishable. At that resolution, I'd probably favor the 460.
On the other hand, if you have any plans to upgrade other components then you should try to take that all into account. For example, if you want to get a 1080p monitor then you should be figuring out what works better for 1080p 60Hz rather than 1366x768 and the RX 470 is clearly better. However, to actually make it all work you'd probably want to upgrade the CPU and, realistically, the best upgrade path is a new CPU, motherboard, and possibly RAM as all modern platforms now use DDR4. It's possible you could find some used hardware for, say, Haswell and pick up a cheap Core i5, pair it with a used or new Haswell-era motherboard, and re-use your DDR3.