Not many info. on the Internet comparing their performance in real world usage, anyone with experience want to comment?
There is no such thing as real world usage, there are thousands of applications in real world and all of them are different.
In general you can build efficient application with both database systems, it is the question of your experience, bias and particular requirements. For example PostgreSQL often handles complex queries better while MySQL has power of multiple storage engines.
As a MySQL expert, what do you think abt the following comments:
MySQL users know firsthand that MySQL is most effective for read-only environments and the web/edge tier - but not for applications in demanding OLTP environments, requiring enterprise-class reliability, availability, and scalability.
It is as usually a lot of marketing talk. In reality you should look into what is important for your particular application and make a choice based on this information.
Too often however people do not like to spend time investigating and simply base decisions on rumors which can be outdated such as “MySQL does not support transactions” or silly “MySQL does not work with tables more than 10.000 rows”
MySQL is not perfect as any other Database Solution but be careful reading marketing talk as it usually only highlights benefits of home made solutions and not speaking about drawbacks.
When It comes to databases I personally follow the rule “whatever works”. Both database engines are scalable, and highly efficient even with large datasets. In reality I guess its hard to compare because you would have to start with some engine, grow database (which make time time), and then switch to different database engine importing data from the old one, which can be a tremendous task to do. It could be a good subject to thesis though :).