I've never used Class::DBI, but a quick look shows that the code for Class::DBI::Column is very simple. It might be worth hacking it to cache the lower-case version of the classname to see if that makes a difference:

use overload
    '""'     => sub { shift->{'name_lc'} },
    fallback => 1;
[...]
sub new {
    my ($class, $name) = @_;
    return $class->SUPER::new(
        {
            name        => $name,
            name_lc     => lc($name),
            _groups     => {},
            placeholder => '?'
        }
    );
}

sub name_lc { shift->{'name_lc'} }
[download]

That should save quite a chunk from the first two lines of your profile output:

%Time    Sec.     #calls   sec/call  F  name
14.67   55.4872  2174052   0.000026     <anon>:...5.8.2/Class/DBI/Colu
+mn.pm:37
 9.55   36.1474  2178574   0.000017     Class::DBI::Column::name_lc
[download]

Be careful though if any other classes are inheriting from CDBI::Column - you'd need to check that this hack is compatible with their expectations. (I'd expect it to be ok though, as long as inheritors call their SUPER::new() to construct.)

Hugo