I'm a newb but I've noticed significantly better downshifting functionality in Ultegra compared to my 105 stuff, and the same guy adjusted both derailleurs. There is a little more hunting for the gear when downshifting on the 105 stuff than Ultegra and that "hunting" is inconsistent from gear to gear. Basically, you have to increase lever-throw on downshifts for the easier gears. I don't know if that's related to the derailer or the shifter.