Migrate MySQL to Ingres

We have a moderately complex PHP web app collecting data from a MySQL database. We've been offered a rather attractive proposition to build an Ingres version (ie. same app, but collects data from an Ingres database). Questions for experts like you: 1) Is this a reasonably straightforward migration in which we can largely replace mysql_query with ingres_query, etc, or will it be more complex than that? 2) Does Ingres compare reasonably well with MySQL in terms of scalability and speed? 3) Any dangers I should be aware of? I am trying to decide whether or not to go forward with this project. Your advice is much appreciated! Thanks, Jeff