I have an 2 year old 11.6" MacBook Air, 1.6G core 2 duo, 4 gigs of ram, it is considerably slower than today's MacBook Air's and Lightroom work is excruciatingly slow. Were I to get a new computer today, I would be thinking about the same choices you want. The solid state drive in the MacBook Air makes it seem to run faster on non-processor intensive tasks and it has a higher resolution screen than the 13" MBP, but the MacBook pro is much faster for processor intensive tasks, and can be outfitted with a solid state drive (it is user upgradeable unlike the MBA) for even better performance. The screen on the MBP is better quality than the one on the Air as far as colours and viewing angle is concerned, but there are 25% fewer pixels, which cuts down your working area when you use photoshop. You just have to decide if the size, lower resolution, and weight of the MBP is worth the extra performance
Personally, I will be waiting until spring when Intel's new Hazwell chips come out. They should give a significant performance boost, coupled with a newer gen Intel HD integrated graphics chip, and maybe even better resolution screens will make it worth the wait for me.
T3i / Tokina 11-16 2.8 / Tamron 17-50 2.8 / Sony Nex-5 / 40mm f/2.8 Pancake / 50mm 1.8 II /100mm f/2.0 / 580 EX II, 2x430 EX II's