In this caliber of Smartphone, you should also consider the HTC Sensation 4G. Out of the box, the dual-core processor is under-clocked. It can be over-clocked to 1.5 GHz without much effort.
I'm the wireless industry and get to play around with these things all time. I've had a week with the Sprint version and like the performance, but prefer the HTC Sense interface over Samsung's TouchWiz. What's holding me back on the SG2S is the 480x800 resolution. Rumor has it that SG3S is around the corner with a much better screen. Don't get me wrong, the SG2S screen looks good, but a phone with a 4.5" screen should have more pixels.
Here is side-by-side comparison over at PhoneArena.com...
http://www.phonearena.com/phones/compare/Samsung-Epic-4G-Touch,HTC-Sensation-4G/phones/5537,5188