DBD::SQLite fastest way to insert multiple rows

I have tried 3 different approaches to inserting multiple (over 500) rows into a SQLite table. Counter-intuitively, approach 3 below is the fastest. I would have assumed approach 2 would be the fastest because it uses a "prepared" statement handle. But my third approach - inserting 500 rows at a time (500 is apparently the max allowed in SQLite) - is way faster.

Am I missing anything? Should I continue with the 500 approach, or is there another way?

note: the below code is not my actual code, I just wrote it here for example purposes and has not been tested.

use strict; 
use warnings;
use DBI;

my $dsn = "DBI:SQLite:dbname=db";
my $dbh = DBI->connect($dsn,"","");

open my $data_file,"<","data.txt"; # 3 integer fields per line

APPROACH_1:
while (<$data_file>) {
    my @fields = split "\t";
    my $insert = join ",", @fields;
    $dbh->do("insert into table values ($insert)";
}

APPROACH_2:
my $sql = "insert into table values (?,?,?)";
my $sth = $dbh->prepare($sql);
while (<$data_file>) {
    my @fields = split "\t";
    $sth->execute(@fields);
}

APPROACH_3:
my @inserts;
while (<$data_file>) {
    my @fields = split "\t";
    my $insert = '('.join ",", @fields.')';
    push @inserts, $insert;
    if (@inserts == 500) {
        my $insert_500 = join ",\n", @inserts;
        $dbh->do("insert into table values $insert_500";
        undef @inserts;
    }
}
# insert leftovers