DB2 express - opinions

Hi all,

I am currently developing an enterprise application (JEE)
working on glassfish.
Currently my team uses free DB2 Express database.
Once we used to use Postgres, but be moved to IBM.
Database holds about 30 000 records (currently biggest table -
of coure will grow - about 100 records daily).
Currently only only thick clients connects to AppServer,
their amount may vary from 10 to, say, 300.
What do you think about migration we made?
Is it senseless or not? In my performance tests I noticed
small performance gains with DB2,
but I wonder what will happen when we'll run out
of the hardware limits of Express edition.
Won't it be better to have Postgres then,
that doesnt have any limits (correct me if I'm wrong) ?
Or is there some other database you would suggest?

Greetings,
Chris