Each processor core run at 2.2 ghz but they have a shared memory controller and bus.. it is this that can cause restriction compared to two single processors running at the same speed in a Symmetric Multi Processing system (SMP) in which case each processor would have its own bus and memory controller... The 4200x2 branding is a PR rating (Performance Rating) and the X2 indicates how many cores the processor has... these numbers are intended to give a better idea of true processor performance as for years, processor manufacturers have described CPUs based on clock speed, typically in megahertz (MHz) or gigahertz (GHz). These speeds provide a simple, straightforward number to rate performance and have been an easy way to rank and compare processors across the industry. But despite its simplicity, clock speed alone isn’t an accurate way to evaluate the overall performance of a computer processor. Processors have many variables – memory bandwidth, file system architecture, cache speed and size, and available headroom, as well as raw CPU power and more..... The processor PR numbers are meant to reflect this - Intel use a different method with the same ideal which actually allows NO comparission at all between processors for the general consumer.

the biggest issue that most people do not realise is that Windows and MS Office do not actually fully support the features offered by these processors... if you run Linux 64 with the correct kernel for your processor the performance hike is dramatic

Overall you generall see about a 30-60%. performance increase in real world terms over a single core processor in the Windows desktop depending upon application support... Its OS and application support thats really letting these processors down at the moment