Until we have as much code written in Rust as is currently implemented in C, experience hasn't shown anything. The same claims and promises have been made for C++ in relation to vanilla C for ages, and it's just not true. An experienced C coder (which arguably takes longer to achieve) will perform as good as a C++ coder of equal skill level. All they do is trade complexity and convenience for simplicity and flexibility; it's a matter of preference, not life and death.