Lenovo Thinkpad X1 has 13,3" and a full powered processor. If you want even bigger you can go with a T420 (14"), which is more similar to the X220 but with a media unit.
Alas the X1 at 13.3" has only the low resolution 1366x768 display and weighs 3.7 lbs and has less battery life than the Mac Air 13.3" which as the higher res 1440x900, weighs 3 lbs and has longer battery life.
Lenovo did not update their "Mac Air" which was the X301. Sadly, like early (pre-2010) versions of the Mac Air it is underpowered (1.4 GHz ULV processor) but it did have the 1440x900 13.3" display. Pity Lenovo did not come out with the update to the X301 using the same processor, screen as the Mac Air.