Well the inline C solution is pretty short, dunno about faster or particularly creative though....

use Inline 'C';

my $str1 = 'foo';
for my $str2( qw( foo bar baz foxtrot perlmonks f ) ) {
    print "'$str1' cmp '$str2' result: ",
        same_scan($str1, $str2) ? "same\n" : "different\n";
}

__END__
__C__
int same_scan(char* str1, char* str2) 
{
  return str1[0] == str2[0] ? 1 : 0;
}

/*

'foo' cmp 'foo' result: same
'foo' cmp 'bar' result: different
'foo' cmp 'baz' result: different
'foo' cmp 'foxtrot' result: same
'foo' cmp 'perlmonks' result: different
'foo' cmp 'f' result: same

*/
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