PostGres compares ok on a lot of workloads, but when the rubber really hits the road that is when it starts to fall apart.
They must fix the TXID ID problem. It will now at least shut down when it is getting close to rolling over, but the vacuum process will just kill your performance in very high transaction workloads. Not that Oracle would not have the same problem if they were using a 32 bit number for the value, but with the size of the ID Oracle uses this won't happen for ~ 140 years.
Immovability... PostGres gets some great performance but it does so at the cost of the data files being so close to the metal that you can't move them to another host that is not exactly the same as it is moving from. If that is not true you have to do an SQLDUMP of the data. That is a fairly fatal flaw in my opinion.
So yes you can use PG in place of Oracle, to a point, but after that point it just does not perform as required.
I migrated a PG DB to Oracle 11g EE and it runs quite smoothly. The application would quickly overwhelm PG without some serious changes to the PG code.