just get an x220.
better screen, cheaper, you can use an m-sata SSD or a normal SSD (might have to be 7mm, so intel or crucial m4 only)...
The x220 is definitely a very worthy option. I have one with the IPS screen, and it is great.
One thing of note is that the colour gamut of the IPS (premium) screen is relatively lacking, and for photo work, you may find that the colour gamut is not large enough. The biggest problem I find with it is that the reds tend to be slightly orangey when compared to the a true sRGB screen. That being said, the x220's colour gamut is superior to the Macbook Air's colour gamut.
YMMV. I do not find this to be a problem except when working with external screens so I can compare the two reds.
On the other hand, just about everything else about the screen (brightness, antiglare, contrast, viewing angles, black levels) are superior to most if not all other 1366x768 screens out there.
The x220 also has much more lifting capacity than the MBA; it runs full power SB processors. I run AutoCAD Civil 3D 2012 on it, and it runs only slightly slower than my i5 2500 desktop on heavy lifting tasks; battery life is reduced by ~33% running CAD under normal use, or basically ~4 hours on a 6 cell (standard) battery. Web browsing and light work will get you ~6 hours. 9 cell = 50% more life.
In the MBA comparison, the MBA has a (vastly) superior trackpad than the x220.
MBA running Windows seems to lose quite a bit of battery life.