Core 2 Duo thermal throttles
Remember the old days when Intel rated Netburst CPU at 3.73GHZ but in reality it often runs at half the speed due the thermal throttling? Same is seemingly happening with Core 2 Duo within normal operating parameters. Basically, you get a Core 2 Duo rated at 2.93GHZ, when it is not doing anything stressful and the room temperature is cold, it runs merry at that speed, most of the circuits are turned off anyway. However, once you add some load, the Intel chip slows down to save itself from meltdown.
BTW, EU may fine Intel $3.5 billion for breaking the law.