Do you really need all 200 columns when you select? If not, you could select only those that you do need and save yourself some bandwidth. Also, I don't know if it's faster than fetchrow_hashref, but I like to use fetch like so when I need access to the columns by name

my @fields = qw(foo bar baz);
my %results;
$sth->execute();
$sth->bind_columns(@results{@fields});
while( $sth->fetch() ) {
   #your results will be available in %results
}
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Maybe I should benchmark it...