Yes, but between a faster CPU and HSPUA radio, the iPhone 4 is noticeably faster 3G in supported areas. I don't know about on WiFi.
The Epic 4g has the same processor as the iPhone 4, a 1-GHz ARM Cortex A8. It has a newer GPU, the PowerVR SGX 540 as opposed to the 535 in the iPhone. It also has 512mB of RAM instead of the 256 in the iPhone. It has a few other advantages, like the Super AMOLED screen, which I can attest is absurdly high in contrast, brightness, saturation, and
Memory fault -- brain fried