This scenario comprises the following FastFormat code, and functional equivalents for all other libraries examined:

    static std::string with_FF_Format(int value)
    {
        std::string str;

        fastformat::fmt(str, "{0}", value);

        return str;
    }

    const int   args[] =
    {
        INT_MIN, -1000, -1, 0, 1, 10, 1000, INT_MAX
    };

    { for(unsigned i = 0; i < ITERATIONS; ++i)
    {
        const int arg = args[i % STLSOFT_NUM_ELEMENTS(args)];

        std::string res = with_FF_Format(arg);
    }}

This is the test/performance/performance.test.one_integer performance test included in the FastFormat 0.2.1 beta 6 distribution.