Thread management inside the JVM process might be less effective than context switching between processes on the OS level. It is better to combine both these technologies to achieve full saturation of resources.

Current CPUs are multicore units. So starting managed servers in the amount of physical cores and pinning them 1:1 to cores will always get the best performance.

By a combination of prioritization of processes on the OS level and Work Manager in WLS, one  could tune the whole environment more precisely.

Assigning more than one managed server to hardware will never bring better performance. 

More instances means more connections to databases, so one could serve more concurrent  calls on the database level. This is primarily why this approach will give better performance numbers.  

Depending on the profile of the application, having more JVMs with smaller heaps will lead to more predictable response times than fewer JVMs with a large heap.

There may be a bottleneck in the application that additional hardware would not solve.

Adding more hardware is costly and time consuming.

Adding hardware at the application layer may place additional load on an already overloaded database, network appliance, or storage system.

Adding more hardware may introduce new configuration requirements that need to be tested.

Store Transaction Logs in a database and use Database stores for JMS to make replication  between sites easier.

Use file based Transaction Logs and JMS stores and implement a separate replication solution  for files in addition to database in case database replication fails.

Implement Oracle RAC at each site to provide a highly available solution within each datacenter.

Configure Whole Server Migration to migrate WebLogic Managed Servers from the primary to the secondary site.

Configure Automatic Service Migration for JMS high availability within a datacenter.

management of many WebLogic Server Domains from a single web console

tracking changes in the configuration of WebLogic Domain

automation of provisioning process in the new environment

checking compliance with the licenses that a customer has

visual creation of JDBC DataSource object to Oracle RAC

isolates WebLogic from RAC changes

has a simple configuration

enables statement caching  

performs faster failure detection and failover

is supported in WebLogic Domain Templates