there are a number of known issues in 6.2.0 that affected performance, all of these are resolved in 6.2.1 (out this week). In addition when we were profiling 6.2.0 we noted a number of places where performance had degraded for various reasons. At present we have a test environment which runs 5.6.7 and a number of 6.x releases (6.0.0, 6.0.1, 6.1.0, 6.2.0, 6.2.1, 6.2.2 at present) and that showed a small drop in performance with 6.0.0 (from 5.6.7) but a large drop with 6.1.0 (this was traced to a piece of code in the client dependancy framework). We've now resolved this and at present 6.2.2 is close to 5.6.7's performance without CDF enabled - when CDF is enabled it supports many more pages per second.

I'd encourage any 6.x users looking for better performance to install 6.2.1 when it's available (backup as usual)

We're continuining to work on performance (6.2.2 is already slightly faster than 6.2.1) and will be integrating the test suite (both load and webtest's) into the build server to ensure that performance remains within expected limits.