Not sure how much difference there is between them optically but having had the old 170-500 and the 150-500 OS, I can say that the OS version was far easier to use - mainly because the OS allows handholding; the weight of the lens alone is enough to make ME think twice about carrying it on the off chance, let alone a tripod as well!
I've just bought a 50-500 non-OS after nearly two years of borrowing one for airshows... Yes if you're used to a kit lens then obviously it's going to be heavy to you but in honesty for a lens with such a good focal range it's a nice small package! My 120-300 weighs more and I'm used to carrying that around race tracks all day
I've had a go with the newer 150-500 OS and the build quality feels a bit plasticy compared to the old one I've got.
Would you say it's worth the extra for the os? How does the non version perform without? I don't miss it on my 70-200 L at all but it is shorter

