What criteria are you using to select your pieces? You love to listen to them? Everyone says that these are impressive in performance? Personally, since I'm going to live with a piece for a while, I try to select pieces which are challenging, but to which I enjoy listening.
Also, what else are your working on? Right now, I'm working on a one Mozart sonata and three shorter pieces by Bach and Chopin. I find if I can work on pieces of different lengths, my practicing is more enjoyable.
The road to "done" on a piece is a long one, so if you're already playing long pieces, why not chose some short ones you'd enjoy.