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/^[056]0+/

/^(?:0|5|6)0+/

use Benchmark 'cmpthese';
my @list = ( '00012345', 'D123470', '0000123450', '0000023456', '50000
+123990' );
...
   charclass => sub { grep /^[056]0+/, @list },
   alt => sub { grep /^(?:0|5|6)0+/, @list },
};

Benchmark: running alt, charclass, each for at least 3 CPU seconds...
       alt:  3 wallclock secs ( 3.00 usr +  0.00 sys =  3.00 CPU) @ 50
+5561.00/s (n=1516683)
...
              Rate       alt charclass
alt       505561/s        --       -5%
charclass 534973/s        6%        --