PostgreSQL vs. Interbase

Hi there.

I'm currently in serious research on what database to use for a B2B site
which is expected to hold millions of records. I have in so far considered
two open source databases - Interbase and PostgreSQL. With this in mind, I'm
sending this email to both the PostgreSQL and Interbase mailing lists and
also on PHP's. I would appreciate what ever information you can provide.
Thanks :)

My inquiry:

Please discuss as to your point of view the advantage of PostgreSQL over
Interbase and/or vise versa. I'm considering three (3) important points

1.  Speed
2.  Data Reliability
3.  Portability

Your messages will be greatly appreciated.