Triggered by some other issues that came up in this thread, I reworked my speed test for access methods. The conclusion might be that when you run your database locally, as in no network delays for databases running on another host, the speed difference between the access methods is huge. fetchrow_hashref should not be used when speed really matters and the number of records visited is relatively big (for one record you won't notice a difference, as the overhead of setting up the handle will make the real fetch work disappear in noise).

Assuming you already prepared your statement handle in $sth, DBI's access-methods are:

HR   while (my $ref = $sth->fetchrow_hashref) {
         # use $ref->{c_base} and $ref->{base}

A    while (my ($c_base, $base) = $sth->fetchrow_array) {
         # use $c_base and $base

AR   while (my $ref = $sth->fetchrow_arrayref) {
         # use $ref->[0] and $ref->[1]

DAR  while (my $ref = DBI::st::fetchrow_arrayref ($sth)) {
         # use $ref->[0] and $ref->[1]

BC   $sth->bind_columns (\my ($c_base, \$base));
     while ($sth->fetch) {
         # use $c_base and $base

DBC  $sth->bind_columns (\my ($c_base, \$base));
     while (DBI::st::fetchrow_arrayref ($sth)) {
         # use $c_base and $base
[download]

When measured against relatively actual installations of the databases, the results are (relative speed, higher is better):

perl-5.18.2-64int-ld    perl-5.16.2-64all-ld
DBI-1.631               DBI-1.631

DBD::Oracle-1.68        DBD::Oracle-1.68
Oracle 12.1.0.1.0       Oracle 11.2.0.3.0
    -> 11.2.0.3.0           -> 11.2.0.3.0
    HR   639                HR   387
   DBC   804                 A  1000
    AR   913                AR  1142
    BC   956               DBC  1186
   DAR   967               DAR  1201
     A   999                BC  1250

DBD::SQLite-1.40        DBD::SQLite-1.40
    HR   255                HR   250
     A  1000                 A  1000
    AR  1041                AR  1172
   DAR  1166               DAR  1244
    BC  1333                BC  1250
   DBC  1455               DBC  1313

DBD::Pg-3.0.0           DBD::Pg-3.0.0
PostgreSQL 9.3.2        PostgreSQL 9.2.4
    HR   198                HR   179
     A  1000                 A  1000
    AR  1143                AR  1279
   DAR  1186               DAR  1281
   DBC  1326                BC  1417
    BC  1332               DBC  1485

DBD::<span style="background:gold">CSV</span>-0.41           DBD::<spa
+n style="background:gold">CSV</span>-0.41
    HR   683                HR   791
     A  1000                 A  1000
    AR  1164                BC  1153
   DAR  1171                AR  1169
    BC  1181               DAR  1176
   DBC  1185               DBC  1186

DBD::mysql-4.025        DBD::mysql-4.026
MariaDB-5.5.33          MariaDB-5.5.33
    HR   102                HR    95
     A   999                 A  1000
    AR  1126                BC  1245
   DAR  1271                AR  1438
    BC  1287               DAR  1509
   DBC  1328               DBC  1612

DBD::Firebird-1.16
firebird-2.5.2.26539
    HR   565
   DAR   991
    AR   997
     A  1000
   DBC  1005
    BC  1179
[download]

As you can see, BC wins over HR by a factor way over 10 on MySQL. YMMV.