I went from a series of fully-loaded 17" Macbook Pros to a fully-loaded 11" Macbook Air a couple years ago and haven't looked back. I do some serious heavy-lifting and never run into performance issues. The portability of it is unbeatable, and you can just get a 27" Thunderbolt display for extra real estate when you're at home or in the office.

Or, like me, you can wait to see whether Apple or Wacom will release a 4k display first and just pick that up with all the money you saved getting an Air instead of an MBP.

Edit:

I should add that my MBA is my personal computer which I use for freelance and contract work. I use a Mac Pro with a 27" Thunderbolt display in the office, but it's overkill until I'm editing HD or UHD video.