efficiency of std::vector for small arrays.

I am currently writing some code where I have a list of objects with a
maximum occupancy of 4. I have been employing std::vector for this but
I was wondering how much overhead is involved. Is it better to use
some other data structure if speed is critical i.e. maybe a struct
like this-

template <typename T>
struct max_four
{
      int element_count;
      T elements[4];
};

Or are std::vectors/lists reasonably competitive in both space/time?

Thanks in advance,

Carter.