An i7 will auto-boost its clock speed (if it's cool enough); it could actually be running at 3.9GHz during your mining. Won't make up twice the work the way, so

An i7 will auto-boost its clock speed (if it's cool enough); it could actually be running at 3.9GHz during your mining. Won't make up twice the work the way, so there's still some architectural improvements, but that's not all the story.