Adding the match_and_tr sub missing from your code:

sub match_and_tr {
  my $string = shift;
  my( $id, $session ) = split( /\./, $string, 2 );
  $id =~ /[a-z]/ and $id =~ tr/a-z/A-Z/;
  return( $id, $session );
}
[download]

I got :

               Rate Old way    Only TR LC
Old way    193050/s         --        -8%
Only TR LC 209205/s         8%         --
               Rate Only TR UC Old way  U
Only TR UC 210084/s         --        -2%
Old way  U 213675/s         2%         --
[download]

Which is as expected. The sub that don't do any tring is of course faster.