I happen to play Rust. I have 300 hours invested in it. The FPS vary by as much as 50%, depending on the server. I have a GTX 1060 6 GB and have the game maxed out in 1080p.
In your situation I would:
Buy, download and install Rust via Steam. See how it performs. If you don't enjoy it, then simply do a Steam return.
* buy 3rd party CPU cooler (Cryorig H7) and upgrade from stock.
* overclock FX-6300 with free AMD Overdrive software
* possibly buy GTX 1060 6 GB.
* sell GTX 960
What is your power supply's manufacturer and model number?