The 50 -140 is a lens with an image quality that almost everyone agrees is excellent. That's why I love it. I like it's constant aperture, quick focus, it's OIS, the weather sealing, and pretty much everything else about it too. The price for what you get isn't too steep for me.
You already know about the image quality of the 55-200, but in other comparisons, the 50-140 is larger, heavier, louder and clunks deep within it's bowels pretty much every time you take a step when the camera is turned off (if you're carrying it around on a neck or shoulder strap). Others may disagree, but I don't think it makes a very good "walking around" or travel lens. It takes more room in your bag and you have to have eaten your Wheaties to be able to carry it around all day, in or out of your bag.
I like the 50-140 in the studio, for portraiture, and when I want to separate subject and background. The OIS makes it easy to hold and shoot, but it excels when on a tripod or monopod. The 55-200 is capable of much of that as well, but it may be, perhaps, better suited for landscape work than the 50-140 or when you want to have it on your camera or available in your bag while shooting out and about.