I love CHICKEN Scheme! Nice to see it mentioned. Though I think it's worth pointing out it compiles to something pretty far from handwritten C, to my understanding. I think this is true of both performance and semantics; for example you can return a pointer to a stack allocated struct from a foreign lambda (this is because chicken's generated C code here doesn't really "return", I think. Not an expert).

Of course you can always drop to manually written C yourself and it's still a fantastic language to interop with C. And CHICKEN 6 (still pre-release) improves upon that! E.g structs and Unions can be returned/passed directly by/to foreign functions, and the new CRUNCH extension/subset is supposed to compile to something quite a bit closer to handwritten C; there are even people experimenting with it on embedded devices.