You'd get a much better speed bump using Inline for at least the "does it have the same digits" check.

No. Chained transliterations are too trivial, any subroutine (or C function) call seems more expensive. Results are not too different with "return 1" line uncommented.

use Inline C => <<'END_OF_C';

int histcmp( SV* sv1, SV* sv2 ) {

    // return 1;

    STRLEN len;
    char* s1 = SvPVbyte( sv1, len );
    char* s2 = SvPVbyte( sv2, len );
    char h1[ 10 ];
    char h2[ 10 ];
    memset( h1, 0, sizeof( h1 ));
    memset( h2, 0, sizeof( h2 ));
    for ( int i = 0; i < len; i ++ ) {
        h1[ s1[ i ] - '0' ] ++;
        h2[ s2[ i ] - '0' ] ++;
    }
    return memcmp( h1, h2, 10 );
}

END_OF_C

sub pwc_c {
    my ( $from, $to, $target ) = @_;
    
    use integer;
    my @witnesses = ([ 4, 7 ], [ 2 .. 9 ]);

    my ( %pairs, $j );
    for ( my $i = ( $from + 2 ) / 3 * 3; $i <= $to; $i += 3 ) {
        my $k = $i % 9 ? 0 : 1;
        
        for ( @{ $witnesses[ $k ]}) {
            last if length( $j = $i * $_ ) != length( $i );
            $pairs{ $i }{ $j } = $_
                unless histcmp( $i, $j )
        }
        for ( @{ $witnesses[ $k ]}) {
            last if length( $j = $i / $_ ) != length( $i );
            $pairs{ $i }{ $j } = -$_
                unless $i % $_
                    || exists $pairs{ $j } && 
                       exists $pairs{ $j }{ $i }
                    || histcmp( $i, $j )
        }
    }
    return scalar grep { %$_ >= $target } values %pairs
}

cmpthese -3, {
    pwc_c => sub { pwc_c( 1500, 2500, 1 )},
    ugly => sub { ugly( 1500, 2500, 1 )},
};
cmpthese -3, {
    pwc_c => sub { pwc_c( 13_427_000, 14_100_000, 2 )},
    ugly => sub { ugly( 13_427_000, 14_100_000, 2 )},
};

#        Rate pwc_c  ugly
# pwc_c 2865/s    --  -12%
# ugly  3251/s   13%    --
#         Rate pwc_c  ugly
# pwc_c 3.42/s    --   -9%
# ugly  3.75/s   10%    --

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In reply to Re^2: Faster (but uglier) PWC 350-2 solutions by Anonymous Monk
in thread Faster (but uglier) PWC 350-2 solutions by Anonymous Monk

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