It was mentioned earlier but not so explicitly: ThinkPad firmware throttles the CPU if the machine is running on a 65W power supply with no battery installed.
See, e.g., http://forums.lenovo.com/t5/X-Series-Tablet-ThinkPad-Laptops/X61-Your-power-adapter-may-be-cheating-you/td-p/17870
It was mentioned earlier but not so explicitly: ThinkPad firmware throttles the CPU if the machine is running on a 65W power supply with no battery installed.
See, e.g., http:// forums. lenovo. com/t5/ X-Series- Tablet- ThinkPad- Laptops/ X61-Your- power-adapter- may-be- cheating- you/td- p/17870