The 50-135 has a very nice size to it. Its very comfortable to cary around on the K-7. As the K-7 is a small camera, you will be kinda holding the lens with a camera attached to it when shooting
It has the 135mm limit though. But its a very nice lens to use for portraits and nature. I used it alot indoors to, works fine when you want to sneek around and take headshoots without beeing close to people.
I could have the 50-135 on the camera around my neck for long periods, but any heavier would have been to much.
Hope it gives some insight, but i havent seen or touched the 60-250 so i cant compare.
But the 50-135 is a very handy size!