head.raku

multi fallback(Any $x) { "a$x" }
multi fallback(Numeric $x) { "n" ~ callsame }
multi fallback(Real $x) { "r" ~ callsame }
multi fallback(Int $x) { "i" ~ callsame }
for ^1_000_000 {
    fallback(4+2i);
    fallback(4.2);
    fallback(42);
}   
say now - INIT now;

new-disp.raku

use nqp;

multi fallback(Any $x) { "a$x" }
multi fallback(Numeric $x) { "n" ~ new-disp-callsame }
multi fallback(Real $x) { "r" ~ new-disp-callsame }
multi fallback(Int $x) { "i" ~ new-disp-callsame }
for ^1_000_000 {
    nqp::dispatch('raku-call', &fallback, 4+2i);
    nqp::dispatch('raku-call', &fallback, 4.2);
    nqp::dispatch('raku-call', &fallback, 42);
}
say now - INIT now;

result

jnthn@homedev:~/dev/rakudo$ ./rakudo-m bench-head.raku 
31.307494412
jnthn@homedev:~/dev/rakudo$ RAKUDO_NEW_DISP=1 ./rakudo-m bench-new-disp.raku 
11.467661091