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

    std::string            arg0           =   "abc";
    const char             arg1[]         =   "def";
    stlsoft::simple_string arg2           =   "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    std::string            arg3(10, '~');
    stlsoft::simple_string arg4           =   "abcdefghijklmnopqrstuvwxyz";
    std::string            arg5           =   "0123456789";
    const char             arg6[]         =   "                                                                        ";
    stlsoft::string_view   arg7(&arg6[0], STLSOFT_NUM_ELEMENTS(arg6) - 1);
    std::string            arg8(1000, '#');
    stlsoft::string_view   arg9           =   arg7;

    std::string  sink;

    fastformat::fmt(sink, "{0}{1}{2}{3}{4}{5}{6}{7}{8}{9}{0}{1}{2}{3}{4}{5}{6}{7}{8}{9}"
                  , arg0, arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8, arg9);

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