Hello gilliann,
As reported before: NO problems in X5 but with X6 YES – on the same computer. I received an announcement e-mail today about this issue, so obviously the performance problem is a common problem. As far as I remember, OS X 10.8 was released before EN X6, so it should have been tested appropriately prior to release. Stop blaming others. Developers need to provide software working in a specific environment, not vice versa.
I hope this clarifies a little.