To answer the question you asked; the breakpoint for performance comes around the 10 cases mark:

#! perl -slw
use strict;
use List::Util qw[ shuffle ];
use Benchmark qw[ cmpthese ];

our %dispatch = (
    'cybox:abcdef' => sub { 1; },
    'cybox:ghijkl' => sub { 1; },
    'cybox:mnopqr' => sub { 1; },
    'cybox:stuvwx' => sub { 1; },
    'cybox:123456' => sub { 1; },
    'cybox:234567' => sub { 1; },
    'cybox:345678' => sub { 1; },
    'cybox:456789' => sub { 1; },
    'cybox:567890' => sub { 1; },
    'cybox:000000' => sub { 1; },
);

our @k = map{ shuffle keys %dispatch } 1 .. 100;

cmpthese -1, {
    a=>q[
        for my $tname ( @k ) {
            $dispatch{ $tname }->();
        }
    ],
    b=>q[
        for my $tname ( @k ) {
            if( $tname eq 'cybox:abcdef' ) {
                1;
            }
            elsif( $tname eq 'cybox:ghijkl' ) {
                1;
            }
            elsif( $tname eq 'cybox:mnopqr' ) {
                1;
            }
            elsif( $tname eq 'cybox:stuvwx' ) {
                1;
            }
            elsif( $tname eq 'cybox:123456' ) {
                1;
            }
            elsif( $tname eq 'cybox:234567' ) {
                1;
            }
            elsif( $tname eq 'cybox:345678' ) {
                1;
            }
            elsif( $tname eq 'cybox:456789' ) {
                1;
            }
            elsif( $tname eq 'cybox:567890' ) {
                1;
            }
            else {
                1;
            }
        }
    ],
};

__END__
C:\test>1149900
    Rate   b   a
b 1810/s  -- -8%
a 1967/s  9%  --

C:\test>\Perl22\bin\perl.exe 1149900.pl
    Rate    b    a
b 2370/s   -- -18%
a 2899/s  22%   --
[download]

Though personally, I tend to gravitate to a dispatch hash when I get 4 or 5 cases or more because it makes for cleaner code.