AnandTech: The iPhone 3GS Hardware Exposed & Analyzed

"The Pre is most definitely faster than the iPhone, but it still has some rough edges. Combine the power of the Pre with the highly optimized software stack of the iPhone and you’ve got the recipe of an extremely fast iPhone."

The Pre has a faster GPU - PowerVR SGX 530 GPU compared to Iphone 3GS PowerVR SGX 520 GPU

Iphone to have a similar CPU to the Pre based on ARM Cortex A8.