I have noticed that many people including me are having problems with Rust on the No HUD case.
I had this issue as well, as low FPS.
I got a solution for it. My machine is a Notebook Lenovo Y580 Which has two GPU`s one is the Intel 4000 HD and the second one is Nvidia GTX 660M. All i did was i went to the visual settings in Windows 7 and than to the Nvidia control panel. Than in the control panel i went to Managing 3d settings (I have the Polish version so) than i picked program settings and than i found the browser that i am using (Google Chrome) and told it to use the Nvidia GPU instead of the Intel one.
I hope this helps you guys, have fun playing.