Rust is well known to not run well on anything. Not sure if it has SLI support at all, something to check, but typically graphics is not the problem, but the CPU. Which, even the fastest CPU has issues running Rust.
Overclocking can certainly hurt your system. You can overheat or overvolt components to the point of failure, or extremely reduce the lifespan of components with too much voltage.
The key is to keep the temperatures and voltages within known limits. For Skylake 1.35 volts is about as high as you want to go on the core, and you want to keep it below 85C, but more ideally 80C.
Late model GPUs are more simple. Nvidia has locked down the voltage so you can't apply more than they recommend. So you can increase the power limit and temperature limit to a certain point and try increasing core and memory offsets. This changes the default boost points. If you encounter instability, you can simply back off a little. What the maximums are vary from card to card, but stock 10 series cards are usually 83C and up to a 115% power limit, more expensive cards may change these limits (on temperature, usually down to control noise)
CPU overclocking is more complex, I recommend looking up some overclocking guides, but 4.5Ghz is certainly relatively easy as a target. But with enough cooling, you can possibly reach 4.6-4.8Ghz.