This information can be found on my blog as well at the link below, along with other useful information.
Resolution: When starting Rust from steam, consider using windowed mode and a resolution just smaller than your screen when you are new to the game. You won’t get as much immersion out of it, but it will make referencing the internet or this guide for help much easier.
Frame Rate Tips: To improve framerate, here are a few things you can try.
press F1 to open your console when connected to a server. Type “grass.on false” without the quotation marks.
Change the video quality settings. This must be done before you connect to a server. Start the game, click Options, change the Graphics “Render Quality” to something lower, then click apply changes. Then log into your favorite server.
Lower your Startup Resolution: If the first two options don’t make the game playable, you probably need to play the game at a lower resolution. Do this when you first start the game from steam, by changing the resolution in the resolution drop down menu before you press play.
Lower Anti-Aliasing: Turn down the Anti-Aliasing of your video card in the video card settings or game profile in your video card software to 2x.