Depends:

1. perl will have a larger startup hit than the C code. If your application doesn't take long to run, that startup time may dwarf the runtime of the entire program. Inline::C will only compound this, at least the first time you run it.
2. does main() do anything? i.e. is there a tight loop where it loads data and passes it to the subroutine? If so, the C code could be faster.
3. is the program runtime bounded by something else, like reading/writing files? If so, the implementation language probably doesn't matter.
4. does the program do something which perl does "naturally" (i.e. internally implemented in highly-tuned C code)? In that case, the perl version may be faster.

As a rule of thumb, when you ask an experience programmer "which language is faster", the answer is probably going to be "whichever language is a more natural way to express the problem".

c.