If you go to beta.cloud.com/#photos you will find that pictures and videos you have uploaded via iCloud Photo Library are NOT the original resolution/size. Pictures are lower resolution, as are videos. That's regardless of whether you're streaming or downloading them. Also regardless of whether you choose to "optimize storage" on your device or keep the originals. This leaves open the possibility that if you are optimizing, you may lose the original files. In other words, once the optimization removes the original file from your phone, there is currently NO WAY to recover that original file. Perhaps when the Photos app for Yosemite releases in 2015, you will be able to download / access the originals. For now, there is no way to do so. Not very reassuring. Just a warning for those thinking about making the jump.