Firstly, I would recommend you always to work with our latest official versions - in this case Q2 2012 SP1 so that you can benefit from all of our improvements, new features and bug fixes.
As for style and template selectors, they will be executed on each item as the corresponding style/template depends on a particular value. The level of performance degradation may vary depending on their definitions - whether you place a heavy control inside the template for example. Could you provide a bit more information about the way you define your style/template selectors ?
All the best,
the Telerik team