I have a 650d, 18-135 stm,55-250mm ef-s & 17-85mm usm ef-s lens.
The stm lens seems on a par in focus speed with the 2 other lenses even the usm one.
Would this be because of the 650d body so on a higher end eos the usm lens would perform better?
I am also interested in the new Sigma 28-250mm so I guess making the 55-250mm & 17-85mm redundent.
I haven't seen anyone answer this, so, I want to at least respond to let you know that someone saw it.
It is my understanding that the 18-135 STM is a new lens and a new motor. It will probably be on par, if not a bit faster, than the USM lenses. I have to admit that I had, but got rid of the 55-255. I didn't like it, the build seemed cheap and the focus always seemed off. I ended up getting rid of it fairly soon.
I don't know anything about the Sigma 28-250. If you do get it, it may replace all of your lenses. However, I would hang on to the 17-85, it is a fantastic lens and may be very useful if you still want to do portraits or something similar.