cmpthese -1,{
    a => q[ my $s = join '', map ''.$_, 1 .. 1e5 ],
    b => q[ my $s = join '', map    $_, 1 .. 1e5 ], 
};;
    Rate    a    b
a 12.3/s   -- -18%
b 14.9/s  21%   --

cmpthese -1,{
    a => q[ my $s = sum map 0+$_, '0001' .. '1000'],
    b => q[ my $s = sum map   $_, '0001' .. '1000'], 
};;
    Rate    b    a
b 1452/s   -- -76%
a 6056/s 317%   --