I went from a 2010 2.4GHz i5 MacBook Pro 15" upgraded to 8Gb and an SSD to a 2013 i7 MBA 13" 8/512 and it was night and day between the two. I was actually quite surprised at how much faster at EVERYTHING the newer MBA was. Stunning difference, really. Just 3 years between them and it wasn't even close.
Now, much of the difference is probably due to the newer PCIe SSD, but GOOD HEAVENS it is drastic. I also think that little Haswell i7 chip is really nice to have with the 8Gb of RAM all in that super thin and light form-factor with an astounding 12-15 hours of battery life. I never looked back. 😀