Yes,
as already stated, the previous Perl solutions compare the content of the files.
Could you try this Perl code and compare its performance with your shell script?

perl -MFile::Find -e'
  $d = shift || die "$0 dir\n";
  find { 
    wanted => sub {
      -f and push @{$u{$_}}, $File::Find::name;
      }
    }, $d;
  @{$u{$_}} > 1 and printf "found %s in: \n\n%s\n\n", 
    $_, join $/, @{$u{$_}} for keys %u;    
  ' <dirname>