It could but who cares, depending on what you currently have it could still be a big improvement and the CPU holding it back won't hurt anything. I'd get it then get a aftermarket cooler for that 6300 and overclock the CPU as far as it will safely go, this will help reduce the bottleneck.
It will bottle neck with a fx 6300 yes, That CPU has shit IPC and won't keep up.
Could still be worth to pick it up though, it could offer more performance than what you are using now. And you can always upgrade Your mobo / CPU later on to something that isn't out dated.
It could but who cares, depending on what you currently have it could still be a big improvement and the CPU holding it back won't hurt anything. I'd get it then get a aftermarket cooler for that 6300 and overclock the CPU as far as it will safely go, this will help reduce the bottleneck.
It's surely a bottleneck to 3.5GHz stock frequency. I tried in these days since I bought a RX 480 video card.
I had mini stuttering experience with The Witcher 3 in FullHD with everything in Ultra except for Hairworks (disabled) and vegetation distance/density at High.
I pushed my FX6300 to 3.8GHz by increasing multiplier and disabling the turbo mode. Also I disabled the Thermal Throttle feature in the BIOS since I have a Tower Heatsink (I have Asrock N68-VS3-FX).
Now I have stable 60fps in the wilderness and villages and sometime it drops at 50fps in Novigrad and Oxenfurt.