Well, back when I was stationed in southern CA and tooling around tracks, drag strips, and Bonneville anyway, I experienced my first frame-mounted fairings. The feeling "touched my soul", so to speak, so I added one to my old streeter, a '69 750cc Norton Commando (she was also the NHRA C-Stock record holder for a while, pre-fairing).
I've had H-bar fairings too and, as I'm sure you know better than me, they have a bit of "personality" themselves. That said, my '07 Road King still had a little bit of the old HD "hinge in the middle" wander - already totally controllable in '07 but still there.
Either way, I frankly believe that a scoot with a windshield only is an entirely different deal when compared to any fairing, pure street or otherwise. I'm also positive my '07 RK handled damn well. I think that any lingering (modest) wander in corners with my '07 had nothing to do with a (relatively speaking) narrow windshield.
However, IMHO, the new frame is what makes the most difference to me. Oh well... no matter what makes us feel (or not feel) some sort of change, these days I'm telling my buds that I just got a new 800 pound Norton.