To go or not to go with Sybase?

My dear all, I am writing to ask for your "success stories" with PHP3/4+Sybase. I have a client who insists on not going with MySQL (same old misconceptions about it) and feels Sybase is more powerful and solid. I may agree, but for our job (the web site which uses PHPLIB session support) and some very simple queries (but numerous) I feel I would go with MySQL. I have not much experience with Sybase, but I remember there was a poor support on it *compared* with MySQL, regarding bug fixes and such. I would like to hear from those who can say "we use it in production, and are very happy, serving n thousands clients/day". If I want to be persuasive, what would be the top 3 arguments of MySQL vs. Sybase, to be used with PHP4 (I hope to convince them least for PHP4). Thank you in advance. -- teodor