You might try the following on for size:

#!/usr/bin/perl
use File::Find qw(find);

kill_big_files( "/tmp", 300*1024 );

sub kill_big_files {
  my $dir  = shift;
  my $size = shift;
  find( sub {
    # current file is in $_
    # current dir is the directory $_ is in

    return if -d; # skip directories
    return if -l; # skip links
    return if $size > -s;

    print "removing $_\n";
    unlink;
  }, $dir);
}
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File::Find is a very useful tool. Very fast for making utilities which recurse directories.