WILL my athlon x4 750k (overclocked at 4g) bootleneck a rx 460?

Solution
Looks like you will be okay. Went to 3DMark and looked for a x4 750K build, here is the link.

http://www.3dmark.com/spy/441883

This build has a R9 270X which is in the same tier as the RX 460. The Graphics and CPU score about the same so they are well matched. As well, this build is only running at stock for the CPU so your 4GHz overclock should allow for even more headroom for the GPU. You could probably get a GTX 1050 Ti or a GTX 960 and still be okay.
Looks like you will be okay. Went to 3DMark and looked for a x4 750K build, here is the link.

http://www.3dmark.com/spy/441883

This build has a R9 270X which is in the same tier as the RX 460. The Graphics and CPU score about the same so they are well matched. As well, this build is only running at stock for the CPU so your 4GHz overclock should allow for even more headroom for the GPU. You could probably get a GTX 1050 Ti or a GTX 960 and still be okay.
 
Solution