What problem are you trying to solve? If your 50 is for your lowlight ride type stuff, it will work. It wouldn't be my first choice (I have the Sigma 30), but it will work. There are some on this forum that swear by the 50. You have all the good-light focal lengths covered. Those lenses can work in some lowlight conditions depending on the camera you have. The 55-250 will work great at AK for the Safari ride and outside shows where the 18-55 is too short. Several years ago I did a weeks vacation at WDW with the 18-55 and a 50-200. I got some great images from that vacation. The question I always ask is, what shots are you trying to get that you can't get with what you have?