Put a 190 on your S4.
Then when you go back to a 180 you'll feel like it's diving into corners with no effort at all.
Correct me if I'm wrong (I may be), but I always thought that the opposite would be true. Sure you can squeeze a 190 onto the OEM S4 rim, but you are doing just that; Squeezing it on. This would make the tire's center contact patch smaller + its leaned-over patch bigger (think of a "V" versus a "U"), thus making the 190 feel like it wants to dive in more than the 180 on the same rim. Of course if you ran a wider rim to accomodate the 190, then yeah, it would be a little more sluggish. Just throwin' it out there...
I noticed the same thing when riding my S4 compared to a friends carbie M750 though. That bike felt SO small + nimble compared to mine, and it probably had a lot to do w/the 160 versus the 180 rear tire. One thing that
really seemed to help me though, was adding a set of clip-ons. The stock bar height on the S4 was a little too high for my liking, and I noticed that getting myself a bit more hunched over really made the bike handle closer to how I want it to. Ideally, I'd also like to raise the rear ride height, but it seems to be one of those things I talk about but will never actually get around to!!