Good news: the customer is running benchmark tests on a system with 64 cores (4x4650 with 8 cores) and 768GB RAM. A monster VM scales fine up to 28vCPUs now and only drops to performance of 24 cores with 32vCPUs. We haven't run yet the application, but it looks like that in this case Hyperthreading (HT) on the previous machine didn't work well. We are looking for the vSphere 5.5 release to try advanced features as well to apply best practices for Oracle tuning on a VMware VM. As posted earlier the document on VMware's Oracle landing page seems to be outdated (2011) so hope to find more recent hints and tips. Will post any new findings.