I'm putting some 16's on my 07 fxstc right now. I considered taller ones but after sitting on a number of bikes I decided that for longer distances I'd prefer that my hands not be (much) higher than my shoulders... too tiring being way up there. To each their own... the 16's and the ergonomics of my bike were just a combo that felt good to me.
You wont regret the 16s on your fxstc, it really completes the look of our bikes in my opinion.
No issues with seeing what's going on around me. I'm 6'4" with 38" sleeve lengths, so the 18"s with a 1.5" riser are good for me, though I wouldn't want them any higher. More comfortable than drag bars to me until you ride on a very windy day or at 70mph+ speeds........then you do fatigue more quickly as part of your arm strength is just holding on. For longer trips or interstate riding I switch to my Gunfighter saddle with the backrest......then it's like resting on the couch; no arm strength used for holding on......your backrest does the work.
Mine at shoulder height.. I do move my head a bit commin up on intersections.. Just habit from riden with apes 35 years.. Helps ta relocate yer signals to yer triple trees to..