If you look around, the difference between the i5 and i7 on Air is negligible even though it's $300 apart. i3 to i5 makes bigger difference for smaller difference in price.
The Air upgrades, as I recall, were dual core i3 to quad core i5 to quad core i7. The quad core i5 is obviously the best one for the price. Though the i7 is only $150 over that, which was only worth it to me for the quicker shipping.
