It's difficult getting a maxed out MBA here.
The only option I have is MBA 4GB SSD128GB.
Not big enough, right?
My second Mac after I switched was a MBA with 1.6 GHz C2D processor. LR was a bit slower on the MBA than on a MBP with a twice faster processor (I don't really use PS), but PM was as fast as on any other computer - actually I found it to run smoother on my Macs than on any Windows machine.
You may come short of the 4GB RAM and 128 SSD. If you can afford it, the bigger processor, bigger RAM and larger SSD would add a lot.
I too had 128 GB SSD and I was always on the edge and I had to keep doing cleanup to make space. Now I have a 256 GB SSD in my MBP and even this fills up way faster than I would prefer. However it is up to your needs and possibilities.
I use RAW files and some times (not always) I make 50-100 GB a day that means it could be tight to keep a day's work on a 128GB and it's much easier with the 256GB. I daily backup them to an external hard drive but this takes an extra hard drive to pack with the computer (and another one for redundant backup) and it adds extra time to the workflow to back up every day to make room for the new photos.
I think especially with disk space the bigger is always the better.
I've been considering to buy an extra 64-128GB USB stick in a small size, but the more compact size ones are slow (USB2) and it would take longer to use them as extra storage.
