I don't understand how people don't realize that 17mm is wide angle... It comes out to ~28mm. That's perfect for landscapes. I shoot the grand majority of my film landscapes at 28mm.
Going any wider is practically retarded, especially when most people have no clue how to use a UWA. If you're going wider than an effective 24mm FOV, and you don't understand how to compose a wide angle shot, then you shouldn't be spending money on another god damn lens... If you're doing indoor video, and your'e trying to capture the space, then sure, the 11-16 is fucking awesome, but by in large, unnessesary for the gran majority of photography.
Stick with your 17-50. It's fast. It covers all the right focal lengths, and it works well at the wide end for landscape. Do some distortion correction in post if you absolutely require it.
Have a nice day, Bluename.