Is there a difference? Yes. Is there a
noticable difference? No. Key word being
noticable. If a single grain of salt is important, Anadtech's tests show that a similarly spec'd 17 has slightly more power than a 15. Same goes for a similarly spec'd 11 i7 to a 13 i7 MBA. Must have something to do with the throttle and/or hyperthreading differences due to the heat from the different sized enclosures (?). But as sure as the dawn, you won't notice these differences. A grain of salt difference in a huge bowl. If you have the cash, won't mind the size/weight and would prefer bigger screen real estate and resolution, the bigger brother is always the bada$$!