Max string length constraint?

I'm able to easily use a string containing 100,000,000, characters.

Can you post example code, and the error messages you are receiving?

If there is a limit, I am guessing it is dbi:sybase, rather than perl that is hitting it.

Something you might try is using $dbh->do() rather than preparing and then executing the statement. It wouldn't suprise me if the driver had a limit of what it could store as a prepared statement.