Hi,
Don't be fooled by "pancake" sticker on the 27mm lens. I had Canon 5DmkIII at the time I bought 27mm lens and my XT-1. After first five shots with it, I decided to sell my whole Canon gear! And I knew what Canon was able to, since before mkIII, I had also mkII, and 1DmkIII, and some great lenses like 135/2.0, 70-200/2.8 etc...
27mm is a great lens, similarly, I would really like to have something like 23mm/2.8