Both will run it smoothly, but the Intel is definitely faster... because the Phenom II was never even set at competing with the Core i7... it was just meant to match/beat the Core 2 Quads and give AM2 users a good CPU upgrade path...
No, clock speeds don't matter, and that 2.8ghz would probably apply to a Pentium D.... (slowest dual-core, and a Core i7 would be like 1.2ghz would be as fast as a 2.8ghz Pentium D)